Files
hello-algo/chapter_backtracking/permutations_problem/index.html
krahets 27bf1548b5 deploy
2026-11-05 01:48:11 +08:00

3208 lines
349 KiB
HTML
Raw Blame History

This file contains invisible Unicode characters
This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
<!DOCTYPE html>
<html class="no-js" lang="zh">
<head>
<meta charset="utf-8"/>
<meta content="width=device-width,initial-scale=1" name="viewport"/>
<meta content="动画图解、一键运行的数据结构与算法教程" name="description"/>
<meta content="krahets" name="author"/>
<link href="https://www.hello-algo.com/chapter_backtracking/permutations_problem/" rel="canonical"/>
<link href="../backtracking_algorithm/" rel="prev"/>
<link href="../subset_sum_problem/" rel="next"/>
<link href="/chapter_backtracking/permutations_problem/" hreflang="zh" rel="alternate"/>
<link href="/zh-hant/chapter_backtracking/permutations_problem/" hreflang="zh-Hant" rel="alternate"/>
<link href="/en/chapter_backtracking/permutations_problem/" hreflang="en" rel="alternate"/>
<link href="/ja/chapter_backtracking/permutations_problem/" hreflang="ja" rel="alternate"/>
<link href="/ru/chapter_backtracking/permutations_problem/" hreflang="ru" rel="alternate"/>
<link href="/ko/chapter_backtracking/permutations_problem/" hreflang="ko" rel="alternate"/>
<link href="../../assets/images/favicon.png" rel="icon"/>
<meta content="zensical-0.0.51" name="generator"/>
<title>13.2 全排列问题 - Hello 算法</title>
<link href="../../assets/stylesheets/modern/main.62c9b9cc.min.css" rel="stylesheet"/>
<link href="../../assets/stylesheets/modern/palette.dfe2e883.min.css" rel="stylesheet"/>
<style>:root{--md-text-font:"Noto Sans SC";--md-code-font:"JetBrains Mono"}</style>
<link href="../../stylesheets/extra.css" rel="stylesheet"/>
<link href="../../stylesheets/animation_player.css" rel="stylesheet"/>
<script>__md_scope=new URL("../..",location),__md_scope.pathname.endsWith("/")||(__md_scope=new URL(__md_scope.pathname+"/",location)),__md_hash=e=>[...e].reduce(((e,t)=>(e<<5)-e+t.charCodeAt(0)),0),__md_get=(e,t=localStorage,_=__md_scope)=>JSON.parse(t.getItem(_.pathname+"."+e)),__md_set=(e,t,_=localStorage,a=__md_scope)=>{try{_.setItem(a.pathname+"."+e,JSON.stringify(t))}catch(e){}},document.documentElement.setAttribute("data-platform",navigator.platform)</script>
<script data-ha-shared-palette="1">
/* Share only the palette across language roots; other preferences stay scoped. */
(() => {
const get = __md_get;
const set = __md_set;
const shared = new URL("/", location);
__md_get = (key, storage = localStorage, scope = __md_scope) => {
if (key !== "__palette") return get(key, storage, scope);
let value = get(key, storage, shared);
// Adopt the current language's old preference only if none is shared yet.
if (value === null && scope.pathname !== shared.pathname) {
value = get(key, storage, scope);
if (value !== null) set(key, value, storage, shared);
}
return value;
};
__md_set = (key, value, storage = localStorage, scope = __md_scope) =>
set(key, value, storage, key === "__palette" ? shared : scope);
})();
</script>
<link href="/assets/figure-svg/css/5632068fdac847e7b03f598e.css" rel="stylesheet"/><link href="/assets/figure-svg/css/9f909651eeceaf5c7dda140d.css" rel="stylesheet"/></head>
<body data-md-color-accent="teal" data-md-color-primary="white" data-md-color-scheme="default" dir="ltr">
<input autocomplete="off" class="md-toggle" data-md-toggle="drawer" id="__drawer" type="checkbox"/>
<input autocomplete="off" class="md-toggle" data-md-toggle="search" id="__search" type="checkbox"/>
<label aria-label="导航栏" class="md-overlay" for="__drawer"></label>
<div data-md-component="skip">
<a class="md-skip" href="#132">
跳转至
</a>
</div>
<div data-md-component="announce">
<aside class="md-banner">
<div class="md-banner__inner md-grid md-typeset">
<div class="banner-svg">
<svg viewbox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><!--!Font Awesome Free 6.5.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free Copyright 2024 Fonticons, Inc.-->
<path d="M480 32c0-12.9-7.8-24.6-19.8-29.6s-25.7-2.2-34.9 6.9L381.7 53c-48 48-113.1 75-181 75H192 160 64c-35.3 0-64 28.7-64 64v96c0 35.3 28.7 64 64 64l0 128c0 17.7 14.3 32 32 32h64c17.7 0 32-14.3 32-32V352l8.7 0c67.9 0 133 27 181 75l43.6 43.6c9.2 9.2 22.9 11.9 34.9 6.9s19.8-16.6 19.8-29.6V300.4c18.6-8.8 32-32.5 32-60.4s-13.4-51.6-32-60.4V32zm-64 76.7V240 371.3C357.2 317.8 280.5 288 200.7 288H192V192h8.7c79.8 0 156.5-29.8 215.3-83.3z"></path>
</svg>
<span>纸质书已发行,详情请见<a href="/chapter_paperbook/">这里</a></span>
</div>
</div>
</aside>
</div>
<header class="md-header md-header--shadow" data-md-component="header">
<nav aria-label="页眉" class="md-header__inner md-grid">
<a aria-label="Hello 算法" class="md-header__button md-logo" data-md-component="logo" href="../.." title="Hello 算法">
<img alt="Hello 算法" src="../../assets/images/logo.svg"/>
</a>
<label aria-label="导航栏" class="md-header__button md-icon" for="__drawer">
<svg class="lucide lucide-menu" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M4 5h16M4 12h16M4 19h16"></path></svg>
</label>
<div class="md-header__title" data-md-component="header-title">
<div class="md-header__ellipsis">
<div class="md-header__topic">
<span class="md-ellipsis">
Hello 算法
</span>
</div>
<div class="md-header__topic" data-md-component="header-topic">
<span class="md-ellipsis">
13.2   全排列问题
</span>
</div>
</div>
</div>
<form class="md-header__option" data-md-component="palette">
<input aria-label="深色模式" class="md-option" data-md-color-accent="teal" data-md-color-media="none" data-md-color-primary="white" data-md-color-scheme="default" id="__palette_0" name="__palette" type="radio"/>
<label class="md-header__button md-icon" for="__palette_1" hidden="" title="深色模式">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M7.5 2c-1.79 1.15-3 3.18-3 5.5s1.21 4.35 3.03 5.5C4.46 13 2 10.54 2 7.5A5.5 5.5 0 0 1 7.5 2m11.57 1.5 1.43 1.43L4.93 20.5 3.5 19.07zm-6.18 2.43L11.41 5 9.97 6l.42-1.7L9 3.24l1.75-.12.58-1.65L12 3.1l1.73.03-1.35 1.13zm-3.3 3.61-1.16-.73-1.12.78.34-1.32-1.09-.83 1.36-.09.45-1.29.51 1.27 1.36.03-1.05.87zM19 13.5a5.5 5.5 0 0 1-5.5 5.5c-1.22 0-2.35-.4-3.26-1.07l7.69-7.69c.67.91 1.07 2.04 1.07 3.26m-4.4 6.58 2.77-1.15-.24 3.35zm4.33-2.7 1.15-2.77 2.2 2.54zm1.15-4.96-1.14-2.78 3.34.24zM9.63 18.93l2.77 1.15-2.53 2.19z"></path></svg>
</label>
<input aria-label="浅色模式" class="md-option" data-md-color-accent="teal" data-md-color-media="none" data-md-color-primary="black" data-md-color-scheme="slate" id="__palette_1" name="__palette" type="radio"/>
<label class="md-header__button md-icon" for="__palette_0" hidden="" title="浅色模式">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M7.5 2c-1.79 1.15-3 3.18-3 5.5s1.21 4.35 3.03 5.5C4.46 13 2 10.54 2 7.5A5.5 5.5 0 0 1 7.5 2m11.57 1.5 1.43 1.43L4.93 20.5 3.5 19.07zm-6.18 2.43L11.41 5 9.97 6l.42-1.7L9 3.24l1.75-.12.58-1.65L12 3.1l1.73.03-1.35 1.13zm-3.3 3.61-1.16-.73-1.12.78.34-1.32-1.09-.83 1.36-.09.45-1.29.51 1.27 1.36.03-1.05.87zM19 13.5a5.5 5.5 0 0 1-5.5 5.5c-1.22 0-2.35-.4-3.26-1.07l7.69-7.69c.67.91 1.07 2.04 1.07 3.26m-4.4 6.58 2.77-1.15-.24 3.35zm4.33-2.7 1.15-2.77 2.2 2.54zm1.15-4.96-1.14-2.78 3.34.24zM9.63 18.93l2.77 1.15-2.53 2.19z"></path></svg>
</label>
</form>
<script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script>
<div class="md-header__option">
<div class="md-select">
<button aria-label="选择当前语言" class="md-header__button md-icon">
<svg class="lucide lucide-languages" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m5 8 6 6M4 14l6-6 2-3M2 5h12M7 2h1M22 22l-5-10-5 10M14 18h6"></path></svg>
</button>
<div class="md-select__inner">
<ul class="md-select__list">
<li class="md-select__item">
<a class="md-select__link" href="/chapter_backtracking/permutations_problem/" hreflang="zh">
简体中文
</a>
</li>
<li class="md-select__item">
<a class="md-select__link" href="/zh-hant/chapter_backtracking/permutations_problem/" hreflang="zh-Hant">
繁體中文
</a>
</li>
<li class="md-select__item">
<a class="md-select__link" href="/en/chapter_backtracking/permutations_problem/" hreflang="en">
English
</a>
</li>
<li class="md-select__item">
<a class="md-select__link" href="/ja/chapter_backtracking/permutations_problem/" hreflang="ja">
日本語
</a>
</li>
<li class="md-select__item">
<a class="md-select__link" href="/ru/chapter_backtracking/permutations_problem/" hreflang="ru">
Русский
</a>
</li>
<li class="md-select__item">
<a class="md-select__link" href="/ko/chapter_backtracking/permutations_problem/" hreflang="ko">
한국어
</a>
</li>
</ul>
</div>
</div>
</div>
<label aria-label="查找" class="md-header__button md-icon" for="__search">
<svg class="lucide lucide-search" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m21 21-4.34-4.34"></path><circle cx="11" cy="11" r="8"></circle></svg>
</label>
<div aria-label="查找" class="md-search" data-md-component="search" role="dialog">
<button class="md-search__button" type="button">
查找
</button>
</div>
<div class="md-header__source">
<a class="md-source" data-md-component="source" href="https://github.com/krahets/hello-algo" title="前往仓库">
<div class="md-source__icon md-icon">
<svg viewbox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><!--! Font Awesome Free 7.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2" fill="currentColor"></path></svg>
</div>
<div class="md-source__repository">
krahets/hello-algo
</div>
</a>
</div>
</nav>
</header>
<div class="md-container" data-md-component="container">
<main class="md-main" data-md-component="main">
<div class="md-main__inner md-grid">
<div class="md-sidebar md-sidebar--primary" data-md-component="sidebar" data-md-type="navigation">
<div class="md-sidebar__scrollwrap">
<div class="md-sidebar__inner">
<nav aria-label="导航栏" class="md-nav md-nav--primary" data-md-level="0">
<label class="md-nav__title" for="__drawer">
<a aria-label="Hello 算法" class="md-nav__button md-logo" data-md-component="logo" href="../.." title="Hello 算法">
<img alt="Hello 算法" src="../../assets/images/logo.svg"/>
</a>
Hello 算法
</label>
<div class="md-nav__source">
<a class="md-source" data-md-component="source" href="https://github.com/krahets/hello-algo" title="前往仓库">
<div class="md-source__icon md-icon">
<svg viewbox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><!--! Font Awesome Free 7.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2" fill="currentColor"></path></svg>
</div>
<div class="md-source__repository">
krahets/hello-algo
</div>
</a>
</div>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_1" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_hello_algo/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m13.13 22.19-1.63-3.83c1.57-.58 3.04-1.36 4.4-2.27zM5.64 12.5l-3.83-1.63 6.1-2.77C7 9.46 6.22 10.93 5.64 12.5M19.22 4c.28 0 .53 0 .74.05.17 1.39-.02 4.25-3.3 7.53-1.7 1.71-3.73 3.02-6.01 3.89l-2.15-2.1c.92-2.31 2.23-4.34 3.92-6.03C15.18 4.58 17.64 4 19.22 4m0-2c-1.98 0-4.98.69-8.22 3.93-2.19 2.19-3.5 4.6-4.35 6.71-.28.75-.09 1.57.46 2.13l2.13 2.12c.38.38.89.61 1.42.61.23 0 .47-.06.7-.15A19.1 19.1 0 0 0 18.07 13c5.66-5.66 3.54-10.61 3.54-10.61S20.7 2 19.22 2m-4.68 7.46c-.78-.78-.78-2.05 0-2.83s2.05-.78 2.83 0c.77.78.78 2.05 0 2.83s-2.05.78-2.83 0m-5.66 7.07-1.41-1.41zM6.24 22l3.64-3.64c-.34-.09-.67-.24-.97-.45L4.83 22zM2 22h1.41l4.77-4.76-1.42-1.41L2 20.59zm0-2.83 4.09-4.08c-.21-.3-.36-.62-.45-.97L2 17.76z"></path></svg>
<span class="md-ellipsis">
序
</span>
</a>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_1_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_1">
<span class="md-nav__icon md-icon"></span>
序
</label>
<ul class="md-nav__list" data-md-scrollfix="">
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_2" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_preface/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M21 4H3a2 2 0 0 0-2 2v13a2 2 0 0 0 2 2h18a2 2 0 0 0 2-2V6a2 2 0 0 0-2-2M3 19V6h8v13zm18 0h-8V6h8zm-7-9.5h6V11h-6zm0 2.5h6v1.5h-6zm0 2.5h6V16h-6z"></path></svg>
<span class="md-ellipsis">
第 0 章   前言
</span>
</a>
<label class="md-nav__link" for="__nav_2" id="__nav_2_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_2_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_2">
<span class="md-nav__icon md-icon"></span>
第 0 章   前言
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_preface/about_the_book/">
<span class="md-ellipsis">
0.1   关于本书
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_preface/suggestions/">
<span class="md-ellipsis">
0.2   如何使用本书
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_preface/summary/">
<span class="md-ellipsis">
0.3   小结
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_3" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_introduction/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M19 3H5c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h14c1.1 0 2-.9 2-2V5c0-1.1-.9-2-2-2m0 16H5V5h14zM6.2 7.7h5v1.5h-5zm6.8 8.1h5v1.5h-5zm0-2.6h5v1.5h-5zM8 18h1.5v-2h2v-1.5h-2v-2H8v2H6V16h2zm6.1-7.1 1.4-1.4 1.4 1.4 1.1-1-1.4-1.4L18 7.1 16.9 6l-1.4 1.4L14.1 6 13 7.1l1.4 1.4L13 9.9z"></path></svg>
<span class="md-ellipsis">
第 1 章   初识算法
</span>
</a>
<label class="md-nav__link" for="__nav_3" id="__nav_3_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_3_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_3">
<span class="md-nav__icon md-icon"></span>
第 1 章   初识算法
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_introduction/algorithms_are_everywhere/">
<span class="md-ellipsis">
1.1   算法无处不在
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_introduction/what_is_dsa/">
<span class="md-ellipsis">
1.2   算法是什么
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_introduction/summary/">
<span class="md-ellipsis">
1.3   小结
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_4" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_computational_complexity/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M6 2h12v6l-4 4 4 4v6H6v-6l4-4-4-4zm10 14.5-4-4-4 4V20h8zm-4-5 4-4V4H8v3.5zM10 6h4v.75l-2 2-2-2z"></path></svg>
<span class="md-ellipsis">
第 2 章   复杂度分析
</span>
</a>
<label class="md-nav__link" for="__nav_4" id="__nav_4_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_4_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_4">
<span class="md-nav__icon md-icon"></span>
第 2 章   复杂度分析
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_computational_complexity/performance_evaluation/">
<span class="md-ellipsis">
2.1   算法效率评估
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_computational_complexity/iteration_and_recursion/">
<span class="md-ellipsis">
2.2   迭代与递归
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_computational_complexity/time_complexity/">
<span class="md-ellipsis">
2.3   时间复杂度
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_computational_complexity/space_complexity/">
<span class="md-ellipsis">
2.4   空间复杂度
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_computational_complexity/summary/">
<span class="md-ellipsis">
2.5   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_computational_complexity/exercises/">
<span class="md-ellipsis">
2.6   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_5" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_data_structure/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M11 13.5v8H3v-8zm-2 2H5v4h4zM12 2l5.5 9h-11zm0 3.86L10.08 9h3.84zM17.5 13c2.5 0 4.5 2 4.5 4.5S20 22 17.5 22 13 20 13 17.5s2-4.5 4.5-4.5m0 2a2.5 2.5 0 0 0-2.5 2.5 2.5 2.5 0 0 0 2.5 2.5 2.5 2.5 0 0 0 2.5-2.5 2.5 2.5 0 0 0-2.5-2.5"></path></svg>
<span class="md-ellipsis">
第 3 章   数据结构
</span>
</a>
<label class="md-nav__link" for="__nav_5" id="__nav_5_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_5_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_5">
<span class="md-nav__icon md-icon"></span>
第 3 章   数据结构
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_data_structure/classification_of_data_structure/">
<span class="md-ellipsis">
3.1   数据结构分类
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_data_structure/basic_data_types/">
<span class="md-ellipsis">
3.2   基本数据类型
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_data_structure/number_encoding/">
<span class="md-ellipsis">
3.3   数字编码 *
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_data_structure/character_encoding/">
<span class="md-ellipsis">
3.4   字符编码 *
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_data_structure/summary/">
<span class="md-ellipsis">
3.5   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_data_structure/exercises/">
<span class="md-ellipsis">
3.6   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_6" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M3 5v14h17V5zm4 2v2H5V7zm-2 6v-2h2v2zm0 2h2v2H5zm13 2H9v-2h9zm0-4H9v-2h9zm0-4H9V7h9z"></path></svg>
<span class="md-ellipsis">
第 4 章   数组与链表
</span>
</a>
<label class="md-nav__link" for="__nav_6" id="__nav_6_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_6_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_6">
<span class="md-nav__icon md-icon"></span>
第 4 章   数组与链表
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/array/">
<span class="md-ellipsis">
4.1   数组
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/linked_list/">
<span class="md-ellipsis">
4.2   链表
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/list/">
<span class="md-ellipsis">
4.3   列表
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/ram_and_cache/">
<span class="md-ellipsis">
4.4   内存与缓存 *
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/summary/">
<span class="md-ellipsis">
4.5   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_array_and_linkedlist/exercises/">
<span class="md-ellipsis">
4.6   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_7" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_stack_and_queue/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M17.36 20.2v-5.38h1.79V22H3v-7.18h1.8v5.38zM6.77 14.32l.37-1.76 8.79 1.85-.37 1.76zm1.16-4.21.76-1.61 8.14 3.78-.76 1.62zm2.26-3.99 1.15-1.38 6.9 5.76-1.15 1.37zm4.45-4.25L20 9.08l-1.44 1.07-5.36-7.21zM6.59 18.41v-1.8h8.98v1.8z"></path></svg>
<span class="md-ellipsis">
第 5 章   栈与队列
</span>
</a>
<label class="md-nav__link" for="__nav_7" id="__nav_7_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_7_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_7">
<span class="md-nav__icon md-icon"></span>
第 5 章   栈与队列
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_stack_and_queue/stack/">
<span class="md-ellipsis">
5.1   栈
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_stack_and_queue/queue/">
<span class="md-ellipsis">
5.2   队列
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_stack_and_queue/deque/">
<span class="md-ellipsis">
5.3   双向队列
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_stack_and_queue/summary/">
<span class="md-ellipsis">
5.4   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_stack_and_queue/exercises/">
<span class="md-ellipsis">
5.5   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_8" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_hashing/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M19.3 17.89c1.32-2.1.7-4.89-1.41-6.21a4.52 4.52 0 0 0-6.21 1.41C10.36 15.2 11 18 13.09 19.3c1.47.92 3.33.92 4.8 0L21 22.39 22.39 21zm-2-.62c-.98.98-2.56.97-3.54 0-.97-.98-.97-2.56.01-3.54.97-.97 2.55-.97 3.53 0 .96.99.95 2.57-.03 3.54zM19 4H5a2 2 0 0 0-2 2v12a2 2 0 0 0 2 2h5.81a6.3 6.3 0 0 1-1.31-2H5v-4h4.18c.16-.71.43-1.39.82-2H5V8h6v2.81a6.3 6.3 0 0 1 2-1.31V8h6v2a6.499 6.499 0 0 1 2 2V6a2 2 0 0 0-2-2"></path></svg>
<span class="md-ellipsis">
第 6 章   哈希表
</span>
</a>
<label class="md-nav__link" for="__nav_8" id="__nav_8_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_8_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_8">
<span class="md-nav__icon md-icon"></span>
第 6 章   哈希表
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_hashing/hash_map/">
<span class="md-ellipsis">
6.1   哈希表
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_hashing/hash_collision/">
<span class="md-ellipsis">
6.2   哈希冲突
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_hashing/hash_algorithm/">
<span class="md-ellipsis">
6.3   哈希算法
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_hashing/summary/">
<span class="md-ellipsis">
6.4   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_hashing/exercises/">
<span class="md-ellipsis">
6.5   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_9" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_tree/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M19.5 17c-.14 0-.26 0-.39.04L17.5 13.8c.45-.45.75-1.09.75-1.8a2.5 2.5 0 0 0-2.5-2.5c-.14 0-.25 0-.4.04L13.74 6.3c.47-.46.76-1.09.76-1.8a2.5 2.5 0 0 0-5 0c0 .7.29 1.34.76 1.79L8.65 9.54c-.15-.04-.26-.04-.4-.04a2.5 2.5 0 0 0-2.5 2.5c0 .71.29 1.34.75 1.79l-1.61 3.25C4.76 17 4.64 17 4.5 17a2.5 2.5 0 0 0 0 5A2.5 2.5 0 0 0 7 19.5c0-.7-.29-1.34-.76-1.79l1.62-3.25c.14.04.26.04.39.04s.25 0 .38-.04l1.63 3.25c-.47.45-.76 1.09-.76 1.79a2.5 2.5 0 0 0 5 0A2.5 2.5 0 0 0 12 17c-.13 0-.26 0-.39.04L10 13.8c.45-.45.75-1.09.75-1.8 0-.7-.29-1.33-.75-1.79l1.61-3.25c.13.04.26.04.39.04s.26 0 .39-.04L14 10.21a2.5 2.5 0 0 0 1.75 4.29c.13 0 .25 0 .38-.04l1.63 3.25c-.47.45-.76 1.09-.76 1.79a2.5 2.5 0 0 0 5 0 2.5 2.5 0 0 0-2.5-2.5m-15 3.5c-.55 0-1-.45-1-1s.45-1 1-1 1 .45 1 1-.45 1-1 1m8.5-1c0 .55-.45 1-1 1s-1-.45-1-1 .45-1 1-1 1 .45 1 1M7.25 12c0-.55.45-1 1-1s1 .45 1 1-.45 1-1 1-1-.45-1-1M11 4.5c0-.55.45-1 1-1s1 .45 1 1-.45 1-1 1-1-.45-1-1m3.75 7.5c0-.55.45-1 1-1s1 .45 1 1-.45 1-1 1-1-.45-1-1m4.75 8.5c-.55 0-1-.45-1-1s.45-1 1-1 1 .45 1 1-.45 1-1 1"></path></svg>
<span class="md-ellipsis">
第 7 章   树
</span>
</a>
<label class="md-nav__link" for="__nav_9" id="__nav_9_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_9_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_9">
<span class="md-nav__icon md-icon"></span>
第 7 章   树
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/binary_tree/">
<span class="md-ellipsis">
7.1   二叉树
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/binary_tree_traversal/">
<span class="md-ellipsis">
7.2   二叉树遍历
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/array_representation_of_tree/">
<span class="md-ellipsis">
7.3   二叉树数组表示
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/binary_search_tree/">
<span class="md-ellipsis">
7.4   二叉搜索树
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/avl_tree/">
<span class="md-ellipsis">
7.5   AVL 树 *
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/summary/">
<span class="md-ellipsis">
7.6   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_tree/exercises/">
<span class="md-ellipsis">
7.7   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_10" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_heap/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M12 1a2.5 2.5 0 0 0-2.5 2.5A2.5 2.5 0 0 0 11 5.79V7H7a2 2 0 0 0-2 2v.71A2.5 2.5 0 0 0 3.5 12 2.5 2.5 0 0 0 5 14.29V15H4a2 2 0 0 0-2 2v1.21A2.5 2.5 0 0 0 .5 20.5 2.5 2.5 0 0 0 3 23a2.5 2.5 0 0 0 2.5-2.5A2.5 2.5 0 0 0 4 18.21V17h4v1.21a2.5 2.5 0 0 0-1.5 2.29A2.5 2.5 0 0 0 9 23a2.5 2.5 0 0 0 2.5-2.5 2.5 2.5 0 0 0-1.5-2.29V17a2 2 0 0 0-2-2H7v-.71A2.5 2.5 0 0 0 8.5 12 2.5 2.5 0 0 0 7 9.71V9h10v.71A2.5 2.5 0 0 0 15.5 12a2.5 2.5 0 0 0 1.5 2.29V15h-1a2 2 0 0 0-2 2v1.21a2.5 2.5 0 0 0-1.5 2.29A2.5 2.5 0 0 0 15 23a2.5 2.5 0 0 0 2.5-2.5 2.5 2.5 0 0 0-1.5-2.29V17h4v1.21a2.5 2.5 0 0 0-1.5 2.29A2.5 2.5 0 0 0 21 23a2.5 2.5 0 0 0 2.5-2.5 2.5 2.5 0 0 0-1.5-2.29V17a2 2 0 0 0-2-2h-1v-.71A2.5 2.5 0 0 0 20.5 12 2.5 2.5 0 0 0 19 9.71V9a2 2 0 0 0-2-2h-4V5.79a2.5 2.5 0 0 0 1.5-2.29A2.5 2.5 0 0 0 12 1m0 1.5a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1M6 11a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1m12 0a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1M3 19.5a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1m6 0a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1m6 0a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1m6 0a1 1 0 0 1 1 1 1 1 0 0 1-1 1 1 1 0 0 1-1-1 1 1 0 0 1 1-1"></path></svg>
<span class="md-ellipsis">
第 8 章   堆
</span>
</a>
<label class="md-nav__link" for="__nav_10" id="__nav_10_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_10_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_10">
<span class="md-nav__icon md-icon"></span>
第 8 章   堆
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_heap/heap/">
<span class="md-ellipsis">
8.1   堆
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_heap/build_heap/">
<span class="md-ellipsis">
8.2   建堆操作
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_heap/top_k/">
<span class="md-ellipsis">
8.3   Top-k 问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_heap/summary/">
<span class="md-ellipsis">
8.4   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_heap/exercises/">
<span class="md-ellipsis">
8.5   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_11" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_graph/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m12 5.37-.44-.06L6 14.9c.24.21.4.48.47.78h11.06c.07-.3.23-.57.47-.78l-5.56-9.59zM6.6 16.53l4.28 2.53c.29-.27.69-.43 1.12-.43s.83.16 1.12.43l4.28-2.53zM12 22a1.68 1.68 0 0 1-1.68-1.68l.09-.56-4.3-2.55c-.31.36-.76.58-1.27.58a1.68 1.68 0 0 1-1.68-1.68c0-.79.53-1.45 1.26-1.64V9.36c-.83-.11-1.47-.82-1.47-1.68A1.68 1.68 0 0 1 4.63 6c.55 0 1.03.26 1.34.66l4.41-2.53-.06-.45c0-.93.75-1.68 1.68-1.68s1.68.75 1.68 1.68l-.06.45 4.41 2.53c.31-.4.79-.66 1.34-.66a1.68 1.68 0 0 1 1.68 1.68c0 .86-.64 1.57-1.47 1.68v5.11c.73.19 1.26.85 1.26 1.64a1.68 1.68 0 0 1-1.68 1.68c-.51 0-.96-.22-1.27-.58l-4.3 2.55.09.56A1.68 1.68 0 0 1 12 22M10.8 4.86 6.3 7.44l.02.24c0 .71-.44 1.32-1.06 1.57l.03 5.25zm2.4 0 5.51 9.64.03-5.25c-.62-.25-1.06-.86-1.06-1.57l.02-.24z"></path></svg>
<span class="md-ellipsis">
第 9 章   图
</span>
</a>
<label class="md-nav__link" for="__nav_11" id="__nav_11_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_11_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_11">
<span class="md-nav__icon md-icon"></span>
第 9 章   图
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_graph/graph/">
<span class="md-ellipsis">
9.1   图
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_graph/graph_operations/">
<span class="md-ellipsis">
9.2   图基础操作
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_graph/graph_traversal/">
<span class="md-ellipsis">
9.3   图的遍历
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_graph/summary/">
<span class="md-ellipsis">
9.4   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_graph/exercises/">
<span class="md-ellipsis">
9.5   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_12" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_searching/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m19.31 18.9 3.08 3.1L21 23.39l-3.12-3.07c-.69.43-1.51.68-2.38.68-2.5 0-4.5-2-4.5-4.5s2-4.5 4.5-4.5 4.5 2 4.5 4.5c0 .88-.25 1.71-.69 2.4m-3.81.1a2.5 2.5 0 0 0 0-5 2.5 2.5 0 0 0 0 5M21 4v2H3V4zM3 16v-2h6v2zm0-5V9h18v2h-2.03c-1.01-.63-2.2-1-3.47-1s-2.46.37-3.47 1z"></path></svg>
<span class="md-ellipsis">
第 10 章   搜索
</span>
</a>
<label class="md-nav__link" for="__nav_12" id="__nav_12_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_12_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_12">
<span class="md-nav__icon md-icon"></span>
第 10 章   搜索
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/binary_search/">
<span class="md-ellipsis">
10.1   二分查找
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/binary_search_insertion/">
<span class="md-ellipsis">
10.2   二分查找插入点
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/binary_search_edge/">
<span class="md-ellipsis">
10.3   二分查找边界
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/replace_linear_by_hashing/">
<span class="md-ellipsis">
10.4   哈希优化策略
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/searching_algorithm_revisited/">
<span class="md-ellipsis">
10.5   重识搜索算法
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/summary/">
<span class="md-ellipsis">
10.6   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_searching/exercises/">
<span class="md-ellipsis">
10.7   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_13" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_sorting/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M19 17h3l-4 4-4-4h3V3h2M2 17h10v2H2M6 5v2H2V5m0 6h7v2H2z"></path></svg>
<span class="md-ellipsis">
第 11 章   排序
</span>
</a>
<label class="md-nav__link" for="__nav_13" id="__nav_13_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_13_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_13">
<span class="md-nav__icon md-icon"></span>
第 11 章   排序
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/sorting_algorithm/">
<span class="md-ellipsis">
11.1   排序算法
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/selection_sort/">
<span class="md-ellipsis">
11.2   选择排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/bubble_sort/">
<span class="md-ellipsis">
11.3   冒泡排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/insertion_sort/">
<span class="md-ellipsis">
11.4   插入排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/quick_sort/">
<span class="md-ellipsis">
11.5   快速排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/merge_sort/">
<span class="md-ellipsis">
11.6   归并排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/heap_sort/">
<span class="md-ellipsis">
11.7   堆排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/bucket_sort/">
<span class="md-ellipsis">
11.8   桶排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/counting_sort/">
<span class="md-ellipsis">
11.9   计数排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/radix_sort/">
<span class="md-ellipsis">
11.10   基数排序
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/summary/">
<span class="md-ellipsis">
11.11   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_sorting/exercises/">
<span class="md-ellipsis">
11.12   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_14" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M17 7v2h5V7zM2 9v6h5V9zm10 0v2H9v2h3v2l3-3zm5 2v2h5v-2zm0 4v2h5v-2z"></path></svg>
<span class="md-ellipsis">
第 12 章   分治
</span>
</a>
<label class="md-nav__link" for="__nav_14" id="__nav_14_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_14_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_14">
<span class="md-nav__icon md-icon"></span>
第 12 章   分治
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/divide_and_conquer/">
<span class="md-ellipsis">
12.1   分治算法
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/binary_search_recur/">
<span class="md-ellipsis">
12.2   分治搜索策略
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/build_binary_tree_problem/">
<span class="md-ellipsis">
12.3   构建树问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/hanota_problem/">
<span class="md-ellipsis">
12.4   汉诺塔问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/summary/">
<span class="md-ellipsis">
12.5   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_divide_and_conquer/exercises/">
<span class="md-ellipsis">
12.6   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--active md-nav__item--nested">
<input checked="" class="md-nav__toggle md-toggle" id="__nav_15" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M18 15a3 3 0 0 1 3 3 3 3 0 0 1-3 3 2.99 2.99 0 0 1-2.83-2H14v-2h1.17c.41-1.17 1.52-2 2.83-2m0 2a1 1 0 0 0-1 1 1 1 0 0 0 1 1 1 1 0 0 0 1-1 1 1 0 0 0-1-1m0-9a1.43 1.43 0 0 0 1.43-1.43 1.43 1.43 0 1 0-2.86 0A1.43 1.43 0 0 0 18 8m0-5.43a4 4 0 0 1 4 4C22 9.56 18 14 18 14s-4-4.44-4-7.43a4 4 0 0 1 4-4M8.83 17H10v2H8.83A2.99 2.99 0 0 1 6 21a3 3 0 0 1-3-3c0-1.31.83-2.42 2-2.83V14h2v1.17c.85.3 1.53.98 1.83 1.83M6 17a1 1 0 0 0-1 1 1 1 0 0 0 1 1 1 1 0 0 0 1-1 1 1 0 0 0-1-1M6 3a3 3 0 0 1 3 3c0 1.31-.83 2.42-2 2.83V10H5V8.83A2.99 2.99 0 0 1 3 6a3 3 0 0 1 3-3m0 2a1 1 0 0 0-1 1 1 1 0 0 0 1 1 1 1 0 0 0 1-1 1 1 0 0 0-1-1m5 14v-2h2v2zm-4-6H5v-2h2z"></path></svg>
<span class="md-ellipsis">
第 13 章   回溯
</span>
</a>
<label class="md-nav__link" for="__nav_15" id="__nav_15_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="true" aria-labelledby="__nav_15_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_15">
<span class="md-nav__icon md-icon"></span>
第 13 章   回溯
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../backtracking_algorithm/">
<span class="md-ellipsis">
13.1   回溯算法
</span>
</a>
</li>
<li class="md-nav__item md-nav__item--active">
<label class="md-nav__link md-nav__link--active" for="__toc">
<span class="md-ellipsis">
13.2   全排列问题
</span>
<span class="md-nav__icon md-icon"></span>
</label>
<a class="md-nav__link md-nav__link--active" href="././">
<span class="md-ellipsis">
13.2   全排列问题
</span>
</a>
<nav aria-label="目录" class="md-nav md-nav--secondary">
<label class="md-nav__title" for="__toc">
<span class="md-nav__icon md-icon"></span>
目录
</label>
<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="#1321">
<span class="md-ellipsis">
<span class="md-typeset">
13.2.1   无相等元素的情况
</span>
</span>
</a>
<nav aria-label="13.2.1 无相等元素的情况" class="md-nav">
<ul class="md-nav__list">
<li class="md-nav__item">
<a class="md-nav__link" href="#1">
<span class="md-ellipsis">
<span class="md-typeset">
1.   重复选择剪枝
</span>
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#2">
<span class="md-ellipsis">
<span class="md-typeset">
2.   代码实现
</span>
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#1322">
<span class="md-ellipsis">
<span class="md-typeset">
13.2.2   考虑相等元素的情况
</span>
</span>
</a>
<nav aria-label="13.2.2 考虑相等元素的情况" class="md-nav">
<ul class="md-nav__list">
<li class="md-nav__item">
<a class="md-nav__link" href="#1_1">
<span class="md-ellipsis">
<span class="md-typeset">
1.   相等元素剪枝
</span>
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#2_1">
<span class="md-ellipsis">
<span class="md-typeset">
2.   代码实现
</span>
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#3">
<span class="md-ellipsis">
<span class="md-typeset">
3.   两种剪枝对比
</span>
</span>
</a>
</li>
</ul>
</nav>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../subset_sum_problem/">
<span class="md-ellipsis">
13.3   子集和问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../n_queens_problem/">
<span class="md-ellipsis">
13.4   N 皇后问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../summary/">
<span class="md-ellipsis">
13.5   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../exercises/">
<span class="md-ellipsis">
13.6   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_16" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_dynamic_programming/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M22 15h-2v3c0 1.11-.89 2-2 2h-3v2l-3-3 3-3v2h3v-3h-2l3-3zm0-11v4c0 1.1-.9 2-2 2H10v10c0 1.1-.9 2-2 2H4c-1.1 0-2-.9-2-2V4c0-1.1.9-2 2-2h16c1.1 0 2 .9 2 2M4 8h4V4H4zm0 2v4h4v-4zm4 10v-4H4v4zm6-12V4h-4v4zm6-4h-4v4h4z"></path></svg>
<span class="md-ellipsis">
第 14 章   动态规划
</span>
</a>
<label class="md-nav__link" for="__nav_16" id="__nav_16_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_16_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_16">
<span class="md-nav__icon md-icon"></span>
第 14 章   动态规划
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/intro_to_dynamic_programming/">
<span class="md-ellipsis">
14.1   初探动态规划
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/dp_problem_features/">
<span class="md-ellipsis">
14.2   DP 问题特性
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/dp_solution_pipeline/">
<span class="md-ellipsis">
14.3   DP 解题思路
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/knapsack_problem/">
<span class="md-ellipsis">
14.4   0-1 背包问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/unbounded_knapsack_problem/">
<span class="md-ellipsis">
14.5   完全背包问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/edit_distance_problem/">
<span class="md-ellipsis">
14.6   编辑距离问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/summary/">
<span class="md-ellipsis">
14.7   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_dynamic_programming/exercises/">
<span class="md-ellipsis">
14.8   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_17" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_greedy/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M13 3c3.88 0 7 3.14 7 7 0 2.8-1.63 5.19-4 6.31V21H9v-3H8c-1.11 0-2-.89-2-2v-3H4.5c-.42 0-.66-.5-.42-.81L6 9.66A7.003 7.003 0 0 1 13 3m0-2C8.41 1 4.61 4.42 4.06 8.9L2.5 11h-.03l-.02.03c-.55.76-.62 1.76-.19 2.59.36.69 1 1.17 1.74 1.32V16c0 1.85 1.28 3.42 3 3.87V23h11v-5.5c2.5-1.67 4-4.44 4-7.5 0-4.97-4.04-9-9-9m4 7.83c0 1.54-1.36 2.77-3.42 4.64L13 14l-.58-.53C10.36 11.6 9 10.37 9 8.83c0-1.2.96-2.19 2.16-2.2h.04c.69 0 1.35.31 1.8.83.45-.52 1.11-.83 1.8-.83 1.2-.01 2.2.96 2.2 2.16z"></path></svg>
<span class="md-ellipsis">
第 15 章   贪心
</span>
</a>
<label class="md-nav__link" for="__nav_17" id="__nav_17_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_17_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_17">
<span class="md-nav__icon md-icon"></span>
第 15 章   贪心
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_greedy/greedy_algorithm/">
<span class="md-ellipsis">
15.1   贪心算法
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_greedy/fractional_knapsack_problem/">
<span class="md-ellipsis">
15.2   分数背包问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_greedy/max_capacity_problem/">
<span class="md-ellipsis">
15.3   最大容量问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_greedy/max_product_cutting_problem/">
<span class="md-ellipsis">
15.4   最大切分乘积问题
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_greedy/summary/">
<span class="md-ellipsis">
15.5   小结
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_greedy/exercises/">
<span class="md-ellipsis">
15.6   练习
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_18" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_appendix/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M11 18h2v-2h-2zm1-16A10 10 0 0 0 2 12a10 10 0 0 0 10 10 10 10 0 0 0 10-10A10 10 0 0 0 12 2m0 18c-4.41 0-8-3.59-8-8s3.59-8 8-8 8 3.59 8 8-3.59 8-8 8m0-14a4 4 0 0 0-4 4h2a2 2 0 0 1 2-2 2 2 0 0 1 2 2c0 2-3 1.75-3 5h2c0-2.25 3-2.5 3-5a4 4 0 0 0-4-4"></path></svg>
<span class="md-ellipsis">
第 16 章   附录
</span>
</a>
<label class="md-nav__link" for="__nav_18" id="__nav_18_label" tabindex="0">
<span class="md-nav__icon md-icon"></span>
</label>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_18_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_18">
<span class="md-nav__icon md-icon"></span>
第 16 章   附录
</label>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_appendix/installation/">
<span class="md-ellipsis">
16.1   编程环境安装
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_appendix/contribution/">
<span class="md-ellipsis">
16.2   一起参与创作
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../../chapter_appendix/terminology/">
<span class="md-ellipsis">
16.3   术语表
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_19" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_reference/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M9 3v15h3V3zm3 2 4 13 3-1-4-13zM5 5v13h3V5zM3 19v2h18v-2z"></path></svg>
<span class="md-ellipsis">
参考文献
</span>
</a>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_19_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_19">
<span class="md-nav__icon md-icon"></span>
参考文献
</label>
<ul class="md-nav__list" data-md-scrollfix="">
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" id="__nav_20" type="checkbox"/>
<div class="md-nav__link md-nav__container">
<a class="md-nav__link" href="../../chapter_paperbook/">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m19 2-5 4.5v11l5-4.5zM6.5 5C4.55 5 2.45 5.4 1 6.5v14.66c0 .25.25.5.5.5.1 0 .15-.07.25-.07 1.35-.65 3.3-1.09 4.75-1.09 1.95 0 4.05.4 5.5 1.5 1.35-.85 3.8-1.5 5.5-1.5 1.65 0 3.35.31 4.75 1.06.1.05.15.03.25.03.25 0 .5-.25.5-.5V6.5c-.6-.45-1.25-.75-2-1V19c-1.1-.35-2.3-.5-3.5-.5-1.7 0-4.15.65-5.5 1.5V6.5C10.55 5.4 8.45 5 6.5 5"></path></svg>
<span class="md-ellipsis">
纸质书
</span>
<span class="md-status md-status--new" title="最近添加">
</span>
</a>
</div>
<nav aria-expanded="false" aria-labelledby="__nav_20_label" class="md-nav" data-md-level="1">
<label class="md-nav__title" for="__nav_20">
<span class="md-nav__icon md-icon"></span>
纸质书
</label>
<ul class="md-nav__list" data-md-scrollfix="">
</ul>
</nav>
</li>
</ul>
</nav>
</div>
</div>
</div>
<div class="md-sidebar md-sidebar--secondary" data-md-component="sidebar" data-md-type="toc">
<div class="md-sidebar__scrollwrap">
<input class="md-nav__toggle md-toggle" id="__toc" type="checkbox"/>
<div class="md-sidebar-button__wrapper">
<label class="md-sidebar-button" for="__toc"></label>
</div>
<div class="md-sidebar__inner">
<nav aria-label="目录" class="md-nav md-nav--secondary">
<label class="md-nav__title" for="__toc">
<span class="md-nav__icon md-icon"></span>
目录
</label>
<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="#1321">
<span class="md-ellipsis">
<span class="md-typeset">
13.2.1   无相等元素的情况
</span>
</span>
</a>
<nav aria-label="13.2.1 无相等元素的情况" class="md-nav">
<ul class="md-nav__list">
<li class="md-nav__item">
<a class="md-nav__link" href="#1">
<span class="md-ellipsis">
<span class="md-typeset">
1.   重复选择剪枝
</span>
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#2">
<span class="md-ellipsis">
<span class="md-typeset">
2.   代码实现
</span>
</span>
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#1322">
<span class="md-ellipsis">
<span class="md-typeset">
13.2.2   考虑相等元素的情况
</span>
</span>
</a>
<nav aria-label="13.2.2 考虑相等元素的情况" class="md-nav">
<ul class="md-nav__list">
<li class="md-nav__item">
<a class="md-nav__link" href="#1_1">
<span class="md-ellipsis">
<span class="md-typeset">
1.   相等元素剪枝
</span>
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#2_1">
<span class="md-ellipsis">
<span class="md-typeset">
2.   代码实现
</span>
</span>
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#3">
<span class="md-ellipsis">
<span class="md-typeset">
3.   两种剪枝对比
</span>
</span>
</a>
</li>
</ul>
</nav>
</li>
</ul>
</nav>
</div>
</div>
</div>
<div class="md-content" data-md-component="content">
<article class="md-content__inner md-typeset">
<!-- Tags -->
<!-- Actions -->
<!-- Actions -->
<!-- Edit button -->
<a class="md-content__button md-icon" href="https://github.com/krahets/hello-algo/tree/main/docs/chapter_backtracking/permutations_problem.md" title="编辑此页">
<svg viewbox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><!--! Font Awesome Free 7.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc.--><path d="M441 58.9 453.1 71c9.4 9.4 9.4 24.6 0 33.9L424 134.1 377.9 88 407 58.9c9.4-9.4 24.6-9.4 33.9 0zM209.8 256.2 344 121.9l46.1 46.1-134.3 134.2c-2.9 2.9-6.5 5-10.4 6.1L186.9 325l16.7-58.5c1.1-3.9 3.2-7.5 6.1-10.4zM373.1 25 175.8 222.2c-8.7 8.7-15 19.4-18.3 31.1l-28.6 100c-2.4 8.4-.1 17.4 6.1 23.6s15.2 8.5 23.6 6.1l100-28.6c11.8-3.4 22.5-9.7 31.1-18.3L487 138.9c28.1-28.1 28.1-73.7 0-101.8L474.9 25c-28.1-28.1-73.7-28.1-101.8 0M88 64c-48.6 0-88 39.4-88 88v272c0 48.6 39.4 88 88 88h272c48.6 0 88-39.4 88-88V312c0-13.3-10.7-24-24-24s-24 10.7-24 24v112c0 22.1-17.9 40-40 40H88c-22.1 0-40-17.9-40-40V152c0-22.1 17.9-40 40-40h112c13.3 0 24-10.7 24-24s-10.7-24-24-24z" fill="currentColor"></path></svg>
</a>
<!-- View button -->
<!-- Page content -->
<h1 id="132">13.2   全排列问题<a class="headerlink" href="#132" title="Permanent link"></a></h1>
<p>全排列问题是回溯算法的一个典型应用。它的定义是在给定一个集合(如一个数组或字符串)的情况下,找出其中元素的所有可能的排列。</p>
<p>表 13-2 列举了几个示例数据,包括输入数组和对应的所有排列。</p>
<p align="center"> 表 13-2   全排列示例 </p>
<div class="center-table">
<table>
<thead>
<tr>
<th style="text-align: left;">输入数组</th>
<th style="text-align: left;">所有排列</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: left;"><span class="arithmatex">\([1]\)</span></td>
<td style="text-align: left;"><span class="arithmatex">\([1]\)</span></td>
</tr>
<tr>
<td style="text-align: left;"><span class="arithmatex">\([1, 2]\)</span></td>
<td style="text-align: left;"><span class="arithmatex">\([1, 2], [2, 1]\)</span></td>
</tr>
<tr>
<td style="text-align: left;"><span class="arithmatex">\([1, 2, 3]\)</span></td>
<td style="text-align: left;"><span class="arithmatex">\([1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]\)</span></td>
</tr>
</tbody>
</table>
</div>
<h2 id="1321">13.2.1   无相等元素的情况<a class="headerlink" href="#1321" title="Permanent link"></a></h2>
<div class="admonition question">
<p class="admonition-title">Question</p>
<p>输入一个整数数组,其中不包含重复元素,返回所有可能的排列。</p>
</div>
<p>从回溯算法的角度看,<strong>我们可以把生成排列的过程想象成一系列选择的结果</strong>。假设输入数组为 <span class="arithmatex">\([1, 2, 3]\)</span> ,如果我们先选择 <span class="arithmatex">\(1\)</span> ,再选择 <span class="arithmatex">\(3\)</span> ,最后选择 <span class="arithmatex">\(2\)</span> ,则获得排列 <span class="arithmatex">\([1, 3, 2]\)</span> 。回退表示撤销一个选择,之后继续尝试其他选择。</p>
<p>从回溯代码的角度看,候选集合 <code>choices</code> 是输入数组中的所有元素,状态 <code>state</code> 是直至目前已被选择的元素。请注意,每个元素只允许被选择一次,<strong>因此 <code>state</code> 中的所有元素都应该是唯一的</strong>。</p>
<p>如图 13-5 所示,我们可以将搜索过程展开成一棵递归树,树中的每个节点代表当前状态 <code>state</code> 。从根节点开始,经过三轮选择后到达叶节点,每个叶节点都对应一个排列。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="chapter_backtracking/permutations_problem.assets/permutations_i.png" data-dark-src="/assets/figure-svg/figures/88d218b2a9622655ecbf6d1a.json" data-src="/assets/figure-svg/figures/5eb9788f944381c672023615.json" style=";--figure-ratio:960.0/540.0"><object data="/chapter_backtracking/permutations_problem.assets/permutations_i.svg" data-theme="light" tabindex="-1" type="image/svg+xml">全排列的递归树</object><object data="/chapter_backtracking/permutations_problem.assets/permutations_i.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">全排列的递归树</object></ha-svg-figure></p>
<p align="center"> 图 13-5   全排列的递归树 </p>
<h3 id="1">1.   重复选择剪枝<a class="headerlink" href="#1" title="Permanent link"></a></h3>
<p>为了实现每个元素只被选择一次,我们考虑引入一个布尔型数组 <code>selected</code> ,其中 <code>selected[i]</code> 表示 <code>choices[i]</code> 是否已被选择,并基于它实现以下剪枝操作。</p>
<ul>
<li>在做出选择 <code>choices[i]</code> 后,我们就将 <code>selected[i]</code> 赋值为 <span class="arithmatex">\(\text{True}\)</span> ,代表它已被选择。</li>
<li>遍历选择列表 <code>choices</code> 时,跳过所有已被选择的节点,即剪枝。</li>
</ul>
<p>如图 13-6 所示,假设我们第一轮选择 1 ,第二轮选择 3 ,第三轮选择 2 ,则需要在第二轮剪掉元素 1 的分支,在第三轮剪掉元素 1 和元素 3 的分支。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="chapter_backtracking/permutations_problem.assets/permutations_i_pruning.png" data-dark-src="/assets/figure-svg/figures/5ee39be34bd171b0c003ac19.json" data-src="/assets/figure-svg/figures/d8441de685fdbf27d6d38e32.json" style=";--figure-ratio:960.0/540.0"><object data="/chapter_backtracking/permutations_problem.assets/permutations_i_pruning.svg" data-theme="light" tabindex="-1" type="image/svg+xml">全排列剪枝示例</object><object data="/chapter_backtracking/permutations_problem.assets/permutations_i_pruning.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">全排列剪枝示例</object></ha-svg-figure></p>
<p align="center"> 图 13-6   全排列剪枝示例 </p>
<p>观察图 13-6 发现,该剪枝操作将搜索空间大小从 <span class="arithmatex">\(O(n^n)\)</span> 减小至 <span class="arithmatex">\(O(n!)\)</span> 。</p>
<h3 id="2">2.   代码实现<a class="headerlink" href="#2" title="Permanent link"></a></h3>
<p>想清楚以上信息之后,我们就可以在框架代码中做“完形填空”了。为了缩短整体代码,我们不单独实现框架代码中的各个函数,而是将它们展开在 <code>backtrack()</code> 函数中:</p>
<div class="tabbed-set tabbed-alternate" data-tabs="1:13"><input checked="checked" id="__tabbed_1_1" name="__tabbed_1" type="radio"/><input id="__tabbed_1_2" name="__tabbed_1" type="radio"/><input id="__tabbed_1_3" name="__tabbed_1" type="radio"/><input id="__tabbed_1_4" name="__tabbed_1" type="radio"/><input id="__tabbed_1_5" name="__tabbed_1" type="radio"/><input id="__tabbed_1_6" name="__tabbed_1" type="radio"/><input id="__tabbed_1_7" name="__tabbed_1" type="radio"/><input id="__tabbed_1_8" name="__tabbed_1" type="radio"/><input id="__tabbed_1_9" name="__tabbed_1" type="radio"/><input id="__tabbed_1_10" name="__tabbed_1" type="radio"/><input id="__tabbed_1_11" name="__tabbed_1" type="radio"/><input id="__tabbed_1_12" name="__tabbed_1" type="radio"/><input id="__tabbed_1_13" name="__tabbed_1" type="radio"/><div class="tabbed-labels"><label for="__tabbed_1_1">Python</label><label for="__tabbed_1_2">C++</label><label for="__tabbed_1_3">Java</label><label for="__tabbed_1_4">C#</label><label for="__tabbed_1_5">Go</label><label for="__tabbed_1_6">Swift</label><label for="__tabbed_1_7">JS</label><label for="__tabbed_1_8">TS</label><label for="__tabbed_1_9">Dart</label><label for="__tabbed_1_10">Rust</label><label for="__tabbed_1_11">C</label><label for="__tabbed_1_12">Kotlin</label><label for="__tabbed_1_13">Ruby</label></div>
<div class="tabbed-content">
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.py</span><pre><span></span><code><a href="#__codelineno-0-1" id="__codelineno-0-1" name="__codelineno-0-1"></a><span class="k">def</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span>
<a href="#__codelineno-0-2" id="__codelineno-0-2" name="__codelineno-0-2"></a> <span class="n">state</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">choices</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">selected</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">bool</span><span class="p">],</span> <span class="n">res</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">]]</span>
<a href="#__codelineno-0-3" id="__codelineno-0-3" name="__codelineno-0-3"></a><span class="p">):</span>
<a href="#__codelineno-0-4" id="__codelineno-0-4" name="__codelineno-0-4"></a><span class="w"> </span><span class="sd">"""回溯算法:全排列 I"""</span>
<a href="#__codelineno-0-5" id="__codelineno-0-5" name="__codelineno-0-5"></a> <span class="c1"># 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-0-6" id="__codelineno-0-6" name="__codelineno-0-6"></a> <span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">state</span><span class="p">)</span> <span class="o">==</span> <span class="nb">len</span><span class="p">(</span><span class="n">choices</span><span class="p">):</span>
<a href="#__codelineno-0-7" id="__codelineno-0-7" name="__codelineno-0-7"></a> <span class="n">res</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="nb">list</span><span class="p">(</span><span class="n">state</span><span class="p">))</span>
<a href="#__codelineno-0-8" id="__codelineno-0-8" name="__codelineno-0-8"></a> <span class="k">return</span>
<a href="#__codelineno-0-9" id="__codelineno-0-9" name="__codelineno-0-9"></a> <span class="c1"># 遍历所有选择</span>
<a href="#__codelineno-0-10" id="__codelineno-0-10" name="__codelineno-0-10"></a> <span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">choice</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="n">choices</span><span class="p">):</span>
<a href="#__codelineno-0-11" id="__codelineno-0-11" name="__codelineno-0-11"></a> <span class="c1"># 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-0-12" id="__codelineno-0-12" name="__codelineno-0-12"></a> <span class="k">if</span> <span class="ow">not</span> <span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]:</span>
<a href="#__codelineno-0-13" id="__codelineno-0-13" name="__codelineno-0-13"></a> <span class="c1"># 尝试:做出选择,更新状态</span>
<a href="#__codelineno-0-14" id="__codelineno-0-14" name="__codelineno-0-14"></a> <span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="kc">True</span>
<a href="#__codelineno-0-15" id="__codelineno-0-15" name="__codelineno-0-15"></a> <span class="n">state</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-0-16" id="__codelineno-0-16" name="__codelineno-0-16"></a> <span class="c1"># 进行下一轮选择</span>
<a href="#__codelineno-0-17" id="__codelineno-0-17" name="__codelineno-0-17"></a> <span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span> <span class="n">choices</span><span class="p">,</span> <span class="n">selected</span><span class="p">,</span> <span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-0-18" id="__codelineno-0-18" name="__codelineno-0-18"></a> <span class="c1"># 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-0-19" id="__codelineno-0-19" name="__codelineno-0-19"></a> <span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="kc">False</span>
<a href="#__codelineno-0-20" id="__codelineno-0-20" name="__codelineno-0-20"></a> <span class="n">state</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<a href="#__codelineno-0-21" id="__codelineno-0-21" name="__codelineno-0-21"></a>
<a href="#__codelineno-0-22" id="__codelineno-0-22" name="__codelineno-0-22"></a><span class="k">def</span><span class="w"> </span><span class="nf">permutations_i</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">])</span> <span class="o">-&gt;</span> <span class="nb">list</span><span class="p">[</span><span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">]]:</span>
<a href="#__codelineno-0-23" id="__codelineno-0-23" name="__codelineno-0-23"></a><span class="w"> </span><span class="sd">"""全排列 I"""</span>
<a href="#__codelineno-0-24" id="__codelineno-0-24" name="__codelineno-0-24"></a> <span class="n">res</span> <span class="o">=</span> <span class="p">[]</span>
<a href="#__codelineno-0-25" id="__codelineno-0-25" name="__codelineno-0-25"></a> <span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="o">=</span><span class="p">[],</span> <span class="n">choices</span><span class="o">=</span><span class="n">nums</span><span class="p">,</span> <span class="n">selected</span><span class="o">=</span><span class="p">[</span><span class="kc">False</span><span class="p">]</span> <span class="o">*</span> <span class="nb">len</span><span class="p">(</span><span class="n">nums</span><span class="p">),</span> <span class="n">res</span><span class="o">=</span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-0-26" id="__codelineno-0-26" name="__codelineno-0-26"></a> <span class="k">return</span> <span class="n">res</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.cpp</span><pre><span></span><code><a href="#__codelineno-1-1" id="__codelineno-1-1" name="__codelineno-1-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-1-2" id="__codelineno-1-2" name="__codelineno-1-2"></a><span class="kt">void</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">bool</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-1-3" id="__codelineno-1-3" name="__codelineno-1-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-1-4" id="__codelineno-1-4" name="__codelineno-1-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">size</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">size</span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-1-5" id="__codelineno-1-5" name="__codelineno-1-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<a href="#__codelineno-1-6" id="__codelineno-1-6" name="__codelineno-1-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-1-7" id="__codelineno-1-7" name="__codelineno-1-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-1-8" id="__codelineno-1-8" name="__codelineno-1-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-1-9" id="__codelineno-1-9" name="__codelineno-1-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">size</span><span class="p">();</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-1-10" id="__codelineno-1-10" name="__codelineno-1-10"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-1-11" id="__codelineno-1-11" name="__codelineno-1-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-1-12" id="__codelineno-1-12" name="__codelineno-1-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-1-13" id="__codelineno-1-13" name="__codelineno-1-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-1-14" id="__codelineno-1-14" name="__codelineno-1-14"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<a href="#__codelineno-1-15" id="__codelineno-1-15" name="__codelineno-1-15"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-1-16" id="__codelineno-1-16" name="__codelineno-1-16"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-1-17" id="__codelineno-1-17" name="__codelineno-1-17"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-1-18" id="__codelineno-1-18" name="__codelineno-1-18"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-1-19" id="__codelineno-1-19" name="__codelineno-1-19"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<a href="#__codelineno-1-20" id="__codelineno-1-20" name="__codelineno-1-20"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">pop_back</span><span class="p">();</span>
<a href="#__codelineno-1-21" id="__codelineno-1-21" name="__codelineno-1-21"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-1-22" id="__codelineno-1-22" name="__codelineno-1-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-1-23" id="__codelineno-1-23" name="__codelineno-1-23"></a><span class="p">}</span>
<a href="#__codelineno-1-24" id="__codelineno-1-24" name="__codelineno-1-24"></a>
<a href="#__codelineno-1-25" id="__codelineno-1-25" name="__codelineno-1-25"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-1-26" id="__codelineno-1-26" name="__codelineno-1-26"></a><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">permutationsI</span><span class="p">(</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-1-27" id="__codelineno-1-27" name="__codelineno-1-27"></a><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">;</span>
<a href="#__codelineno-1-28" id="__codelineno-1-28" name="__codelineno-1-28"></a><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">bool</span><span class="o">&gt;</span><span class="w"> </span><span class="n">selected</span><span class="p">(</span><span class="n">nums</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span><span class="w"> </span><span class="nb">false</span><span class="p">);</span>
<a href="#__codelineno-1-29" id="__codelineno-1-29" name="__codelineno-1-29"></a><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-1-30" id="__codelineno-1-30" name="__codelineno-1-30"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-1-31" id="__codelineno-1-31" name="__codelineno-1-31"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-1-32" id="__codelineno-1-32" name="__codelineno-1-32"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.java</span><pre><span></span><code><a href="#__codelineno-2-1" id="__codelineno-2-1" name="__codelineno-2-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-2-2" id="__codelineno-2-2" name="__codelineno-2-2"></a><span class="kt">void</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">[]</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-3" id="__codelineno-2-3" name="__codelineno-2-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-2-4" id="__codelineno-2-4" name="__codelineno-2-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-5" id="__codelineno-2-5" name="__codelineno-2-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="p">(</span><span class="n">state</span><span class="p">));</span>
<a href="#__codelineno-2-6" id="__codelineno-2-6" name="__codelineno-2-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-2-7" id="__codelineno-2-7" name="__codelineno-2-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-2-8" id="__codelineno-2-8" name="__codelineno-2-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-2-9" id="__codelineno-2-9" name="__codelineno-2-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">length</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-10" id="__codelineno-2-10" name="__codelineno-2-10"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="p">;</span>
<a href="#__codelineno-2-11" id="__codelineno-2-11" name="__codelineno-2-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-2-12" id="__codelineno-2-12" name="__codelineno-2-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-13" id="__codelineno-2-13" name="__codelineno-2-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-2-14" id="__codelineno-2-14" name="__codelineno-2-14"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-2-15" id="__codelineno-2-15" name="__codelineno-2-15"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-2-16" id="__codelineno-2-16" name="__codelineno-2-16"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-2-17" id="__codelineno-2-17" name="__codelineno-2-17"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-2-18" id="__codelineno-2-18" name="__codelineno-2-18"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-2-19" id="__codelineno-2-19" name="__codelineno-2-19"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-2-20" id="__codelineno-2-20" name="__codelineno-2-20"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">remove</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="p">()</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
<a href="#__codelineno-2-21" id="__codelineno-2-21" name="__codelineno-2-21"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-2-22" id="__codelineno-2-22" name="__codelineno-2-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-2-23" id="__codelineno-2-23" name="__codelineno-2-23"></a><span class="p">}</span>
<a href="#__codelineno-2-24" id="__codelineno-2-24" name="__codelineno-2-24"></a>
<a href="#__codelineno-2-25" id="__codelineno-2-25" name="__codelineno-2-25"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-2-26" id="__codelineno-2-26" name="__codelineno-2-26"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="nf">permutationsI</span><span class="p">(</span><span class="kt">int</span><span class="o">[]</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-27" id="__codelineno-2-27" name="__codelineno-2-27"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="p">();</span>
<a href="#__codelineno-2-28" id="__codelineno-2-28" name="__codelineno-2-28"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="p">(),</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">boolean</span><span class="o">[</span><span class="n">nums</span><span class="p">.</span><span class="na">length</span><span class="o">]</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-2-29" id="__codelineno-2-29" name="__codelineno-2-29"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-2-30" id="__codelineno-2-30" name="__codelineno-2-30"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.cs</span><pre><span></span><code><a href="#__codelineno-3-1" id="__codelineno-3-1" name="__codelineno-3-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-3-2" id="__codelineno-3-2" name="__codelineno-3-2"></a><span class="k">void</span><span class="w"> </span><span class="nf">Backtrack</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="p">[]</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-3" id="__codelineno-3-3" name="__codelineno-3-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-3-4" id="__codelineno-3-4" name="__codelineno-3-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">Count</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">Length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-5" id="__codelineno-3-5" name="__codelineno-3-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="p">(</span><span class="n">state</span><span class="p">));</span>
<a href="#__codelineno-3-6" id="__codelineno-3-6" name="__codelineno-3-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-3-7" id="__codelineno-3-7" name="__codelineno-3-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-3-8" id="__codelineno-3-8" name="__codelineno-3-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-3-9" id="__codelineno-3-9" name="__codelineno-3-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">Length</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-10" id="__codelineno-3-10" name="__codelineno-3-10"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-3-11" id="__codelineno-3-11" name="__codelineno-3-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-3-12" id="__codelineno-3-12" name="__codelineno-3-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-13" id="__codelineno-3-13" name="__codelineno-3-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-3-14" id="__codelineno-3-14" name="__codelineno-3-14"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">true</span><span class="p">;</span>
<a href="#__codelineno-3-15" id="__codelineno-3-15" name="__codelineno-3-15"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-3-16" id="__codelineno-3-16" name="__codelineno-3-16"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-3-17" id="__codelineno-3-17" name="__codelineno-3-17"></a><span class="w"> </span><span class="n">Backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-3-18" id="__codelineno-3-18" name="__codelineno-3-18"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-3-19" id="__codelineno-3-19" name="__codelineno-3-19"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">false</span><span class="p">;</span>
<a href="#__codelineno-3-20" id="__codelineno-3-20" name="__codelineno-3-20"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">RemoveAt</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">Count</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
<a href="#__codelineno-3-21" id="__codelineno-3-21" name="__codelineno-3-21"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-3-22" id="__codelineno-3-22" name="__codelineno-3-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-3-23" id="__codelineno-3-23" name="__codelineno-3-23"></a><span class="p">}</span>
<a href="#__codelineno-3-24" id="__codelineno-3-24" name="__codelineno-3-24"></a>
<a href="#__codelineno-3-25" id="__codelineno-3-25" name="__codelineno-3-25"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-3-26" id="__codelineno-3-26" name="__codelineno-3-26"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">PermutationsI</span><span class="p">(</span><span class="kt">int</span><span class="p">[]</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-27" id="__codelineno-3-27" name="__codelineno-3-27"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-3-28" id="__codelineno-3-28" name="__codelineno-3-28"></a><span class="w"> </span><span class="n">Backtrack</span><span class="p">([],</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">bool</span><span class="p">[</span><span class="n">nums</span><span class="p">.</span><span class="n">Length</span><span class="p">],</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-3-29" id="__codelineno-3-29" name="__codelineno-3-29"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-3-30" id="__codelineno-3-30" name="__codelineno-3-30"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.go</span><pre><span></span><code><a href="#__codelineno-4-1" id="__codelineno-4-1" name="__codelineno-4-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-4-2" id="__codelineno-4-2" name="__codelineno-4-2"></a><span class="kd">func</span><span class="w"> </span><span class="nx">backtrackI</span><span class="p">(</span><span class="nx">state</span><span class="w"> </span><span class="o">*</span><span class="p">[]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="w"> </span><span class="o">*</span><span class="p">[]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="w"> </span><span class="o">*</span><span class="p">[]</span><span class="kt">bool</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="w"> </span><span class="o">*</span><span class="p">[][]</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-4-3" id="__codelineno-4-3" name="__codelineno-4-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-4-4" id="__codelineno-4-4" name="__codelineno-4-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">choices</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-4-5" id="__codelineno-4-5" name="__codelineno-4-5"></a><span class="w"> </span><span class="nx">newState</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">append</span><span class="p">([]</span><span class="kt">int</span><span class="p">{},</span><span class="w"> </span><span class="o">*</span><span class="nx">state</span><span class="p">...)</span>
<a href="#__codelineno-4-6" id="__codelineno-4-6" name="__codelineno-4-6"></a><span class="w"> </span><span class="o">*</span><span class="nx">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">append</span><span class="p">(</span><span class="o">*</span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">newState</span><span class="p">)</span>
<a href="#__codelineno-4-7" id="__codelineno-4-7" name="__codelineno-4-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-4-8" id="__codelineno-4-8" name="__codelineno-4-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-4-9" id="__codelineno-4-9" name="__codelineno-4-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">choices</span><span class="p">);</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-4-10" id="__codelineno-4-10" name="__codelineno-4-10"></a><span class="w"> </span><span class="nx">choice</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">choices</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span>
<a href="#__codelineno-4-11" id="__codelineno-4-11" name="__codelineno-4-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-4-12" id="__codelineno-4-12" name="__codelineno-4-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="p">(</span><span class="o">*</span><span class="nx">selected</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-4-13" id="__codelineno-4-13" name="__codelineno-4-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-4-14" id="__codelineno-4-14" name="__codelineno-4-14"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">selected</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-4-15" id="__codelineno-4-15" name="__codelineno-4-15"></a><span class="w"> </span><span class="o">*</span><span class="nx">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">append</span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choice</span><span class="p">)</span>
<a href="#__codelineno-4-16" id="__codelineno-4-16" name="__codelineno-4-16"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-4-17" id="__codelineno-4-17" name="__codelineno-4-17"></a><span class="w"> </span><span class="nx">backtrackI</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">)</span>
<a href="#__codelineno-4-18" id="__codelineno-4-18" name="__codelineno-4-18"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-4-19" id="__codelineno-4-19" name="__codelineno-4-19"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">selected</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-4-20" id="__codelineno-4-20" name="__codelineno-4-20"></a><span class="w"> </span><span class="o">*</span><span class="nx">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)[:</span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
<a href="#__codelineno-4-21" id="__codelineno-4-21" name="__codelineno-4-21"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-4-22" id="__codelineno-4-22" name="__codelineno-4-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-4-23" id="__codelineno-4-23" name="__codelineno-4-23"></a><span class="p">}</span>
<a href="#__codelineno-4-24" id="__codelineno-4-24" name="__codelineno-4-24"></a>
<a href="#__codelineno-4-25" id="__codelineno-4-25" name="__codelineno-4-25"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-4-26" id="__codelineno-4-26" name="__codelineno-4-26"></a><span class="kd">func</span><span class="w"> </span><span class="nx">permutationsI</span><span class="p">(</span><span class="nx">nums</span><span class="w"> </span><span class="p">[]</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="p">[][]</span><span class="kt">int</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-4-27" id="__codelineno-4-27" name="__codelineno-4-27"></a><span class="w"> </span><span class="nx">res</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">([][]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
<a href="#__codelineno-4-28" id="__codelineno-4-28" name="__codelineno-4-28"></a><span class="w"> </span><span class="nx">state</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">([]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
<a href="#__codelineno-4-29" id="__codelineno-4-29" name="__codelineno-4-29"></a><span class="w"> </span><span class="nx">selected</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">([]</span><span class="kt">bool</span><span class="p">,</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="nx">nums</span><span class="p">))</span>
<a href="#__codelineno-4-30" id="__codelineno-4-30" name="__codelineno-4-30"></a><span class="w"> </span><span class="nx">backtrackI</span><span class="p">(</span><span class="o">&amp;</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">nums</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">res</span><span class="p">)</span>
<a href="#__codelineno-4-31" id="__codelineno-4-31" name="__codelineno-4-31"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span>
<a href="#__codelineno-4-32" id="__codelineno-4-32" name="__codelineno-4-32"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.swift</span><pre><span></span><code><a href="#__codelineno-5-1" id="__codelineno-5-1" name="__codelineno-5-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-5-2" id="__codelineno-5-2" name="__codelineno-5-2"></a><span class="kd">func</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="kr">inout</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">],</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">],</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="kr">inout</span><span class="w"> </span><span class="p">[</span><span class="nb">Bool</span><span class="p">],</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="kr">inout</span><span class="w"> </span><span class="p">[[</span><span class="nb">Int</span><span class="p">]])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-5-3" id="__codelineno-5-3" name="__codelineno-5-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-5-4" id="__codelineno-5-4" name="__codelineno-5-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="bp">count</span><span class="w"> </span><span class="p">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="bp">count</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-5-5" id="__codelineno-5-5" name="__codelineno-5-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">state</span><span class="p">)</span>
<a href="#__codelineno-5-6" id="__codelineno-5-6" name="__codelineno-5-6"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-5-7" id="__codelineno-5-7" name="__codelineno-5-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-5-8" id="__codelineno-5-8" name="__codelineno-5-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-5-9" id="__codelineno-5-9" name="__codelineno-5-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">enumerated</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-5-10" id="__codelineno-5-10" name="__codelineno-5-10"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-5-11" id="__codelineno-5-11" name="__codelineno-5-11"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-5-12" id="__codelineno-5-12" name="__codelineno-5-12"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-5-13" id="__codelineno-5-13" name="__codelineno-5-13"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-5-14" id="__codelineno-5-14" name="__codelineno-5-14"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-5-15" id="__codelineno-5-15" name="__codelineno-5-15"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-5-16" id="__codelineno-5-16" name="__codelineno-5-16"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-5-17" id="__codelineno-5-17" name="__codelineno-5-17"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-5-18" id="__codelineno-5-18" name="__codelineno-5-18"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-5-19" id="__codelineno-5-19" name="__codelineno-5-19"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="bp">removeLast</span><span class="p">()</span>
<a href="#__codelineno-5-20" id="__codelineno-5-20" name="__codelineno-5-20"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-5-21" id="__codelineno-5-21" name="__codelineno-5-21"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-5-22" id="__codelineno-5-22" name="__codelineno-5-22"></a><span class="p">}</span>
<a href="#__codelineno-5-23" id="__codelineno-5-23" name="__codelineno-5-23"></a>
<a href="#__codelineno-5-24" id="__codelineno-5-24" name="__codelineno-5-24"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-5-25" id="__codelineno-5-25" name="__codelineno-5-25"></a><span class="kd">func</span><span class="w"> </span><span class="nf">permutationsI</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">])</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">[[</span><span class="nb">Int</span><span class="p">]]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-5-26" id="__codelineno-5-26" name="__codelineno-5-26"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">state</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[]</span>
<a href="#__codelineno-5-27" id="__codelineno-5-27" name="__codelineno-5-27"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">selected</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w"> </span><span class="bp">count</span><span class="p">:</span><span class="w"> </span><span class="n">nums</span><span class="p">.</span><span class="bp">count</span><span class="p">)</span>
<a href="#__codelineno-5-28" id="__codelineno-5-28" name="__codelineno-5-28"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">res</span><span class="p">:</span><span class="w"> </span><span class="p">[[</span><span class="nb">Int</span><span class="p">]]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[]</span>
<a href="#__codelineno-5-29" id="__codelineno-5-29" name="__codelineno-5-29"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-5-30" id="__codelineno-5-30" name="__codelineno-5-30"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-5-31" id="__codelineno-5-31" name="__codelineno-5-31"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.js</span><pre><span></span><code><a href="#__codelineno-6-1" id="__codelineno-6-1" name="__codelineno-6-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-6-2" id="__codelineno-6-2" name="__codelineno-6-2"></a><span class="kd">function</span><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-6-3" id="__codelineno-6-3" name="__codelineno-6-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-6-4" id="__codelineno-6-4" name="__codelineno-6-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">state</span><span class="p">.</span><span class="nx">length</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-6-5" id="__codelineno-6-5" name="__codelineno-6-5"></a><span class="w"> </span><span class="nx">res</span><span class="p">.</span><span class="nx">push</span><span class="p">([...</span><span class="nx">state</span><span class="p">]);</span>
<a href="#__codelineno-6-6" id="__codelineno-6-6" name="__codelineno-6-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-6-7" id="__codelineno-6-7" name="__codelineno-6-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-6-8" id="__codelineno-6-8" name="__codelineno-6-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-6-9" id="__codelineno-6-9" name="__codelineno-6-9"></a><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">forEach</span><span class="p">((</span><span class="nx">choice</span><span class="p">,</span><span class="w"> </span><span class="nx">i</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-6-10" id="__codelineno-6-10" name="__codelineno-6-10"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-6-11" id="__codelineno-6-11" name="__codelineno-6-11"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-6-12" id="__codelineno-6-12" name="__codelineno-6-12"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-6-13" id="__codelineno-6-13" name="__codelineno-6-13"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-6-14" id="__codelineno-6-14" name="__codelineno-6-14"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">choice</span><span class="p">);</span>
<a href="#__codelineno-6-15" id="__codelineno-6-15" name="__codelineno-6-15"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-6-16" id="__codelineno-6-16" name="__codelineno-6-16"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-6-17" id="__codelineno-6-17" name="__codelineno-6-17"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-6-18" id="__codelineno-6-18" name="__codelineno-6-18"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-6-19" id="__codelineno-6-19" name="__codelineno-6-19"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">pop</span><span class="p">();</span>
<a href="#__codelineno-6-20" id="__codelineno-6-20" name="__codelineno-6-20"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-6-21" id="__codelineno-6-21" name="__codelineno-6-21"></a><span class="w"> </span><span class="p">});</span>
<a href="#__codelineno-6-22" id="__codelineno-6-22" name="__codelineno-6-22"></a><span class="p">}</span>
<a href="#__codelineno-6-23" id="__codelineno-6-23" name="__codelineno-6-23"></a>
<a href="#__codelineno-6-24" id="__codelineno-6-24" name="__codelineno-6-24"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-6-25" id="__codelineno-6-25" name="__codelineno-6-25"></a><span class="kd">function</span><span class="w"> </span><span class="nx">permutationsI</span><span class="p">(</span><span class="nx">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-6-26" id="__codelineno-6-26" name="__codelineno-6-26"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-6-27" id="__codelineno-6-27" name="__codelineno-6-27"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">([],</span><span class="w"> </span><span class="nx">nums</span><span class="p">,</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">nums</span><span class="p">.</span><span class="nx">length</span><span class="p">).</span><span class="nx">fill</span><span class="p">(</span><span class="kc">false</span><span class="p">),</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-6-28" id="__codelineno-6-28" name="__codelineno-6-28"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span><span class="p">;</span>
<a href="#__codelineno-6-29" id="__codelineno-6-29" name="__codelineno-6-29"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.ts</span><pre><span></span><code><a href="#__codelineno-7-1" id="__codelineno-7-1" name="__codelineno-7-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-7-2" id="__codelineno-7-2" name="__codelineno-7-2"></a><span class="kd">function</span><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span>
<a href="#__codelineno-7-3" id="__codelineno-7-3" name="__codelineno-7-3"></a><span class="w"> </span><span class="nx">state</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span>
<a href="#__codelineno-7-4" id="__codelineno-7-4" name="__codelineno-7-4"></a><span class="w"> </span><span class="nx">choices</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span>
<a href="#__codelineno-7-5" id="__codelineno-7-5" name="__codelineno-7-5"></a><span class="w"> </span><span class="nx">selected</span><span class="o">:</span><span class="w"> </span><span class="kt">boolean</span><span class="p">[],</span>
<a href="#__codelineno-7-6" id="__codelineno-7-6" name="__codelineno-7-6"></a><span class="w"> </span><span class="nx">res</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[][]</span>
<a href="#__codelineno-7-7" id="__codelineno-7-7" name="__codelineno-7-7"></a><span class="p">)</span><span class="o">:</span><span class="w"> </span><span class="ow">void</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-8" id="__codelineno-7-8" name="__codelineno-7-8"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-7-9" id="__codelineno-7-9" name="__codelineno-7-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">state</span><span class="p">.</span><span class="nx">length</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-10" id="__codelineno-7-10" name="__codelineno-7-10"></a><span class="w"> </span><span class="nx">res</span><span class="p">.</span><span class="nx">push</span><span class="p">([...</span><span class="nx">state</span><span class="p">]);</span>
<a href="#__codelineno-7-11" id="__codelineno-7-11" name="__codelineno-7-11"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-7-12" id="__codelineno-7-12" name="__codelineno-7-12"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-7-13" id="__codelineno-7-13" name="__codelineno-7-13"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-7-14" id="__codelineno-7-14" name="__codelineno-7-14"></a><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">forEach</span><span class="p">((</span><span class="nx">choice</span><span class="p">,</span><span class="w"> </span><span class="nx">i</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-15" id="__codelineno-7-15" name="__codelineno-7-15"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-7-16" id="__codelineno-7-16" name="__codelineno-7-16"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-17" id="__codelineno-7-17" name="__codelineno-7-17"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-7-18" id="__codelineno-7-18" name="__codelineno-7-18"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-7-19" id="__codelineno-7-19" name="__codelineno-7-19"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">choice</span><span class="p">);</span>
<a href="#__codelineno-7-20" id="__codelineno-7-20" name="__codelineno-7-20"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-7-21" id="__codelineno-7-21" name="__codelineno-7-21"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-7-22" id="__codelineno-7-22" name="__codelineno-7-22"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-7-23" id="__codelineno-7-23" name="__codelineno-7-23"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-7-24" id="__codelineno-7-24" name="__codelineno-7-24"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">pop</span><span class="p">();</span>
<a href="#__codelineno-7-25" id="__codelineno-7-25" name="__codelineno-7-25"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-7-26" id="__codelineno-7-26" name="__codelineno-7-26"></a><span class="w"> </span><span class="p">});</span>
<a href="#__codelineno-7-27" id="__codelineno-7-27" name="__codelineno-7-27"></a><span class="p">}</span>
<a href="#__codelineno-7-28" id="__codelineno-7-28" name="__codelineno-7-28"></a>
<a href="#__codelineno-7-29" id="__codelineno-7-29" name="__codelineno-7-29"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-7-30" id="__codelineno-7-30" name="__codelineno-7-30"></a><span class="kd">function</span><span class="w"> </span><span class="nx">permutationsI</span><span class="p">(</span><span class="nx">nums</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[])</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[][]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-31" id="__codelineno-7-31" name="__codelineno-7-31"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">res</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[][]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-7-32" id="__codelineno-7-32" name="__codelineno-7-32"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">([],</span><span class="w"> </span><span class="nx">nums</span><span class="p">,</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">nums</span><span class="p">.</span><span class="nx">length</span><span class="p">).</span><span class="nx">fill</span><span class="p">(</span><span class="kc">false</span><span class="p">),</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-7-33" id="__codelineno-7-33" name="__codelineno-7-33"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span><span class="p">;</span>
<a href="#__codelineno-7-34" id="__codelineno-7-34" name="__codelineno-7-34"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.dart</span><pre><span></span><code><a href="#__codelineno-8-1" id="__codelineno-8-1" name="__codelineno-8-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-8-2" id="__codelineno-8-2" name="__codelineno-8-2"></a><span class="kt">void</span><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span>
<a href="#__codelineno-8-3" id="__codelineno-8-3" name="__codelineno-8-3"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">,</span>
<a href="#__codelineno-8-4" id="__codelineno-8-4" name="__codelineno-8-4"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span>
<a href="#__codelineno-8-5" id="__codelineno-8-5" name="__codelineno-8-5"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">bool</span><span class="o">&gt;</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span>
<a href="#__codelineno-8-6" id="__codelineno-8-6" name="__codelineno-8-6"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">,</span>
<a href="#__codelineno-8-7" id="__codelineno-8-7" name="__codelineno-8-7"></a><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-8" id="__codelineno-8-8" name="__codelineno-8-8"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-8-9" id="__codelineno-8-9" name="__codelineno-8-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">length</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-10" id="__codelineno-8-10" name="__codelineno-8-10"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">List</span><span class="p">.</span><span class="n">from</span><span class="p">(</span><span class="n">state</span><span class="p">));</span>
<a href="#__codelineno-8-11" id="__codelineno-8-11" name="__codelineno-8-11"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-8-12" id="__codelineno-8-12" name="__codelineno-8-12"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-8-13" id="__codelineno-8-13" name="__codelineno-8-13"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-8-14" id="__codelineno-8-14" name="__codelineno-8-14"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">length</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-15" id="__codelineno-8-15" name="__codelineno-8-15"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-8-16" id="__codelineno-8-16" name="__codelineno-8-16"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-8-17" id="__codelineno-8-17" name="__codelineno-8-17"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-18" id="__codelineno-8-18" name="__codelineno-8-18"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-8-19" id="__codelineno-8-19" name="__codelineno-8-19"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-8-20" id="__codelineno-8-20" name="__codelineno-8-20"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-8-21" id="__codelineno-8-21" name="__codelineno-8-21"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-8-22" id="__codelineno-8-22" name="__codelineno-8-22"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-8-23" id="__codelineno-8-23" name="__codelineno-8-23"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-8-24" id="__codelineno-8-24" name="__codelineno-8-24"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-8-25" id="__codelineno-8-25" name="__codelineno-8-25"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">removeLast</span><span class="p">();</span>
<a href="#__codelineno-8-26" id="__codelineno-8-26" name="__codelineno-8-26"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-8-27" id="__codelineno-8-27" name="__codelineno-8-27"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-8-28" id="__codelineno-8-28" name="__codelineno-8-28"></a><span class="p">}</span>
<a href="#__codelineno-8-29" id="__codelineno-8-29" name="__codelineno-8-29"></a>
<a href="#__codelineno-8-30" id="__codelineno-8-30" name="__codelineno-8-30"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-8-31" id="__codelineno-8-31" name="__codelineno-8-31"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">permutationsI</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-32" id="__codelineno-8-32" name="__codelineno-8-32"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-8-33" id="__codelineno-8-33" name="__codelineno-8-33"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">([],</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">filled</span><span class="p">(</span><span class="n">nums</span><span class="p">.</span><span class="n">length</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">),</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-8-34" id="__codelineno-8-34" name="__codelineno-8-34"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-8-35" id="__codelineno-8-35" name="__codelineno-8-35"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.rs</span><pre><span></span><code><a href="#__codelineno-9-1" id="__codelineno-9-1" name="__codelineno-9-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-9-2" id="__codelineno-9-2" name="__codelineno-9-2"></a><span class="k">fn</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="k">mut</span><span class="w"> </span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="p">[</span><span class="kt">i32</span><span class="p">],</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="p">[</span><span class="kt">bool</span><span class="p">],</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;&gt;</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-3" id="__codelineno-9-3" name="__codelineno-9-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-9-4" id="__codelineno-9-4" name="__codelineno-9-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-5" id="__codelineno-9-5" name="__codelineno-9-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">push</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<a href="#__codelineno-9-6" id="__codelineno-9-6" name="__codelineno-9-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-9-7" id="__codelineno-9-7" name="__codelineno-9-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-9-8" id="__codelineno-9-8" name="__codelineno-9-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-9-9" id="__codelineno-9-9" name="__codelineno-9-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="mi">0</span><span class="o">..</span><span class="n">choices</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-10" id="__codelineno-9-10" name="__codelineno-9-10"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-9-11" id="__codelineno-9-11" name="__codelineno-9-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-9-12" id="__codelineno-9-12" name="__codelineno-9-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-13" id="__codelineno-9-13" name="__codelineno-9-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-9-14" id="__codelineno-9-14" name="__codelineno-9-14"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-9-15" id="__codelineno-9-15" name="__codelineno-9-15"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">push</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-9-16" id="__codelineno-9-16" name="__codelineno-9-16"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-9-17" id="__codelineno-9-17" name="__codelineno-9-17"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">clone</span><span class="p">(),</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-9-18" id="__codelineno-9-18" name="__codelineno-9-18"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-9-19" id="__codelineno-9-19" name="__codelineno-9-19"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-9-20" id="__codelineno-9-20" name="__codelineno-9-20"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">pop</span><span class="p">();</span>
<a href="#__codelineno-9-21" id="__codelineno-9-21" name="__codelineno-9-21"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-9-22" id="__codelineno-9-22" name="__codelineno-9-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-9-23" id="__codelineno-9-23" name="__codelineno-9-23"></a><span class="p">}</span>
<a href="#__codelineno-9-24" id="__codelineno-9-24" name="__codelineno-9-24"></a>
<a href="#__codelineno-9-25" id="__codelineno-9-25" name="__codelineno-9-25"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-9-26" id="__codelineno-9-26" name="__codelineno-9-26"></a><span class="k">fn</span><span class="w"> </span><span class="nf">permutations_i</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="p">[</span><span class="kt">i32</span><span class="p">])</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-27" id="__codelineno-9-27" name="__codelineno-9-27"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Vec</span><span class="p">::</span><span class="n">new</span><span class="p">();</span><span class="w"> </span><span class="c1">// 状态(子集)</span>
<a href="#__codelineno-9-28" id="__codelineno-9-28" name="__codelineno-9-28"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="nb">Vec</span><span class="p">::</span><span class="n">new</span><span class="p">(),</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="fm">vec!</span><span class="p">[</span><span class="kc">false</span><span class="p">;</span><span class="w"> </span><span class="n">nums</span><span class="p">.</span><span class="n">len</span><span class="p">()],</span><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-9-29" id="__codelineno-9-29" name="__codelineno-9-29"></a><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-9-30" id="__codelineno-9-30" name="__codelineno-9-30"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.c</span><pre><span></span><code><a href="#__codelineno-10-1" id="__codelineno-10-1" name="__codelineno-10-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-10-2" id="__codelineno-10-2" name="__codelineno-10-2"></a><span class="kt">void</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">stateSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">,</span><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="o">*</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">resSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-3" id="__codelineno-10-3" name="__codelineno-10-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-10-4" id="__codelineno-10-4" name="__codelineno-10-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">stateSize</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-5" id="__codelineno-10-5" name="__codelineno-10-5"></a><span class="w"> </span><span class="n">res</span><span class="p">[</span><span class="o">*</span><span class="n">resSize</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">choicesSize</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span>
<a href="#__codelineno-10-6" id="__codelineno-10-6" name="__codelineno-10-6"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-7" id="__codelineno-10-7" name="__codelineno-10-7"></a><span class="w"> </span><span class="n">res</span><span class="p">[</span><span class="o">*</span><span class="n">resSize</span><span class="p">][</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-10-8" id="__codelineno-10-8" name="__codelineno-10-8"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-10-9" id="__codelineno-10-9" name="__codelineno-10-9"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">resSize</span><span class="p">)</span><span class="o">++</span><span class="p">;</span>
<a href="#__codelineno-10-10" id="__codelineno-10-10" name="__codelineno-10-10"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-10-11" id="__codelineno-10-11" name="__codelineno-10-11"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-10-12" id="__codelineno-10-12" name="__codelineno-10-12"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-10-13" id="__codelineno-10-13" name="__codelineno-10-13"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-14" id="__codelineno-10-14" name="__codelineno-10-14"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-10-15" id="__codelineno-10-15" name="__codelineno-10-15"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-10-16" id="__codelineno-10-16" name="__codelineno-10-16"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-17" id="__codelineno-10-17" name="__codelineno-10-17"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-10-18" id="__codelineno-10-18" name="__codelineno-10-18"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<a href="#__codelineno-10-19" id="__codelineno-10-19" name="__codelineno-10-19"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">stateSize</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choice</span><span class="p">;</span>
<a href="#__codelineno-10-20" id="__codelineno-10-20" name="__codelineno-10-20"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-10-21" id="__codelineno-10-21" name="__codelineno-10-21"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">stateSize</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">resSize</span><span class="p">);</span>
<a href="#__codelineno-10-22" id="__codelineno-10-22" name="__codelineno-10-22"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-10-23" id="__codelineno-10-23" name="__codelineno-10-23"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<a href="#__codelineno-10-24" id="__codelineno-10-24" name="__codelineno-10-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-10-25" id="__codelineno-10-25" name="__codelineno-10-25"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-10-26" id="__codelineno-10-26" name="__codelineno-10-26"></a><span class="p">}</span>
<a href="#__codelineno-10-27" id="__codelineno-10-27" name="__codelineno-10-27"></a>
<a href="#__codelineno-10-28" id="__codelineno-10-28" name="__codelineno-10-28"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-10-29" id="__codelineno-10-29" name="__codelineno-10-29"></a><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="nf">permutationsI</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">numsSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">returnSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-30" id="__codelineno-10-30" name="__codelineno-10-30"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">numsSize</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span>
<a href="#__codelineno-10-31" id="__codelineno-10-31" name="__codelineno-10-31"></a><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="o">*</span><span class="n">selected</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">bool</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">numsSize</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">bool</span><span class="p">));</span>
<a href="#__codelineno-10-32" id="__codelineno-10-32" name="__codelineno-10-32"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">numsSize</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-33" id="__codelineno-10-33" name="__codelineno-10-33"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<a href="#__codelineno-10-34" id="__codelineno-10-34" name="__codelineno-10-34"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-10-35" id="__codelineno-10-35" name="__codelineno-10-35"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">MAX_SIZE</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">));</span>
<a href="#__codelineno-10-36" id="__codelineno-10-36" name="__codelineno-10-36"></a><span class="w"> </span><span class="o">*</span><span class="n">returnSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<a href="#__codelineno-10-37" id="__codelineno-10-37" name="__codelineno-10-37"></a>
<a href="#__codelineno-10-38" id="__codelineno-10-38" name="__codelineno-10-38"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">numsSize</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">returnSize</span><span class="p">);</span>
<a href="#__codelineno-10-39" id="__codelineno-10-39" name="__codelineno-10-39"></a>
<a href="#__codelineno-10-40" id="__codelineno-10-40" name="__codelineno-10-40"></a><span class="w"> </span><span class="n">free</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<a href="#__codelineno-10-41" id="__codelineno-10-41" name="__codelineno-10-41"></a><span class="w"> </span><span class="n">free</span><span class="p">(</span><span class="n">selected</span><span class="p">);</span>
<a href="#__codelineno-10-42" id="__codelineno-10-42" name="__codelineno-10-42"></a>
<a href="#__codelineno-10-43" id="__codelineno-10-43" name="__codelineno-10-43"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-10-44" id="__codelineno-10-44" name="__codelineno-10-44"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.kt</span><pre><span></span><code><a href="#__codelineno-11-1" id="__codelineno-11-1" name="__codelineno-11-1"></a><span class="cm">/* 回溯算法:全排列 I */</span>
<a href="#__codelineno-11-2" id="__codelineno-11-2" name="__codelineno-11-2"></a><span class="kd">fun</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span>
<a href="#__codelineno-11-3" id="__codelineno-11-3" name="__codelineno-11-3"></a><span class="w"> </span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;</span><span class="p">,</span>
<a href="#__codelineno-11-4" id="__codelineno-11-4" name="__codelineno-11-4"></a><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="n">IntArray</span><span class="p">,</span>
<a href="#__codelineno-11-5" id="__codelineno-11-5" name="__codelineno-11-5"></a><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">,</span>
<a href="#__codelineno-11-6" id="__codelineno-11-6" name="__codelineno-11-6"></a><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="n">MutableList</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;?&gt;</span>
<a href="#__codelineno-11-7" id="__codelineno-11-7" name="__codelineno-11-7"></a><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-8" id="__codelineno-11-8" name="__codelineno-11-8"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-11-9" id="__codelineno-11-9" name="__codelineno-11-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">size</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-10" id="__codelineno-11-10" name="__codelineno-11-10"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">toMutableList</span><span class="p">())</span>
<a href="#__codelineno-11-11" id="__codelineno-11-11" name="__codelineno-11-11"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-11-12" id="__codelineno-11-12" name="__codelineno-11-12"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-13" id="__codelineno-11-13" name="__codelineno-11-13"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-11-14" id="__codelineno-11-14" name="__codelineno-11-14"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">indices</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-15" id="__codelineno-11-15" name="__codelineno-11-15"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="o">[</span><span class="n">i</span><span class="o">]</span>
<a href="#__codelineno-11-16" id="__codelineno-11-16" name="__codelineno-11-16"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-11-17" id="__codelineno-11-17" name="__codelineno-11-17"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-18" id="__codelineno-11-18" name="__codelineno-11-18"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-11-19" id="__codelineno-11-19" name="__codelineno-11-19"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-11-20" id="__codelineno-11-20" name="__codelineno-11-20"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-11-21" id="__codelineno-11-21" name="__codelineno-11-21"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-11-22" id="__codelineno-11-22" name="__codelineno-11-22"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-11-23" id="__codelineno-11-23" name="__codelineno-11-23"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-11-24" id="__codelineno-11-24" name="__codelineno-11-24"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-11-25" id="__codelineno-11-25" name="__codelineno-11-25"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">removeAt</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">)</span>
<a href="#__codelineno-11-26" id="__codelineno-11-26" name="__codelineno-11-26"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-27" id="__codelineno-11-27" name="__codelineno-11-27"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-28" id="__codelineno-11-28" name="__codelineno-11-28"></a><span class="p">}</span>
<a href="#__codelineno-11-29" id="__codelineno-11-29" name="__codelineno-11-29"></a>
<a href="#__codelineno-11-30" id="__codelineno-11-30" name="__codelineno-11-30"></a><span class="cm">/* 全排列 I */</span>
<a href="#__codelineno-11-31" id="__codelineno-11-31" name="__codelineno-11-31"></a><span class="kd">fun</span><span class="w"> </span><span class="nf">permutationsI</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span><span class="w"> </span><span class="n">IntArray</span><span class="p">):</span><span class="w"> </span><span class="n">MutableList</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;?&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-32" id="__codelineno-11-32" name="__codelineno-11-32"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">mutableListOf</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;?&gt;</span><span class="p">()</span>
<a href="#__codelineno-11-33" id="__codelineno-11-33" name="__codelineno-11-33"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">mutableListOf</span><span class="p">(),</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">(</span><span class="n">nums</span><span class="p">.</span><span class="na">size</span><span class="p">),</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-11-34" id="__codelineno-11-34" name="__codelineno-11-34"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-11-35" id="__codelineno-11-35" name="__codelineno-11-35"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_i.rb</span><pre><span></span><code><a href="#__codelineno-12-1" id="__codelineno-12-1" name="__codelineno-12-1"></a><span class="c1">### 回溯算法:全排列 I ###</span>
<a href="#__codelineno-12-2" id="__codelineno-12-2" name="__codelineno-12-2"></a><span class="k">def</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-12-3" id="__codelineno-12-3" name="__codelineno-12-3"></a><span class="w"> </span><span class="c1"># 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-12-4" id="__codelineno-12-4" name="__codelineno-12-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">state</span><span class="o">.</span><span class="n">length</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="o">.</span><span class="n">length</span>
<a href="#__codelineno-12-5" id="__codelineno-12-5" name="__codelineno-12-5"></a><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">state</span><span class="o">.</span><span class="n">dup</span>
<a href="#__codelineno-12-6" id="__codelineno-12-6" name="__codelineno-12-6"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-12-7" id="__codelineno-12-7" name="__codelineno-12-7"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-12-8" id="__codelineno-12-8" name="__codelineno-12-8"></a>
<a href="#__codelineno-12-9" id="__codelineno-12-9" name="__codelineno-12-9"></a><span class="w"> </span><span class="c1"># 遍历所有选择</span>
<a href="#__codelineno-12-10" id="__codelineno-12-10" name="__codelineno-12-10"></a><span class="w"> </span><span class="n">choices</span><span class="o">.</span><span class="n">each_with_index</span><span class="w"> </span><span class="k">do</span><span class="w"> </span><span class="o">|</span><span class="n">choice</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="o">|</span>
<a href="#__codelineno-12-11" id="__codelineno-12-11" name="__codelineno-12-11"></a><span class="w"> </span><span class="c1"># 剪枝:不允许重复选择元素</span>
<a href="#__codelineno-12-12" id="__codelineno-12-12" name="__codelineno-12-12"></a><span class="w"> </span><span class="k">unless</span><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span>
<a href="#__codelineno-12-13" id="__codelineno-12-13" name="__codelineno-12-13"></a><span class="w"> </span><span class="c1"># 尝试:做出选择,更新状态</span>
<a href="#__codelineno-12-14" id="__codelineno-12-14" name="__codelineno-12-14"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kp">true</span>
<a href="#__codelineno-12-15" id="__codelineno-12-15" name="__codelineno-12-15"></a><span class="w"> </span><span class="n">state</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">choice</span>
<a href="#__codelineno-12-16" id="__codelineno-12-16" name="__codelineno-12-16"></a><span class="w"> </span><span class="c1"># 进行下一轮选择</span>
<a href="#__codelineno-12-17" id="__codelineno-12-17" name="__codelineno-12-17"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-12-18" id="__codelineno-12-18" name="__codelineno-12-18"></a><span class="w"> </span><span class="c1"># 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-12-19" id="__codelineno-12-19" name="__codelineno-12-19"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kp">false</span>
<a href="#__codelineno-12-20" id="__codelineno-12-20" name="__codelineno-12-20"></a><span class="w"> </span><span class="n">state</span><span class="o">.</span><span class="n">pop</span>
<a href="#__codelineno-12-21" id="__codelineno-12-21" name="__codelineno-12-21"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-12-22" id="__codelineno-12-22" name="__codelineno-12-22"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-12-23" id="__codelineno-12-23" name="__codelineno-12-23"></a><span class="k">end</span>
<a href="#__codelineno-12-24" id="__codelineno-12-24" name="__codelineno-12-24"></a>
<a href="#__codelineno-12-25" id="__codelineno-12-25" name="__codelineno-12-25"></a><span class="c1">### 全排列 I ###</span>
<a href="#__codelineno-12-26" id="__codelineno-12-26" name="__codelineno-12-26"></a><span class="k">def</span><span class="w"> </span><span class="nf">permutations_i</span><span class="p">(</span><span class="n">nums</span><span class="p">)</span>
<a href="#__codelineno-12-27" id="__codelineno-12-27" name="__codelineno-12-27"></a><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">[]</span>
<a href="#__codelineno-12-28" id="__codelineno-12-28" name="__codelineno-12-28"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="o">[]</span><span class="p">,</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="nb">Array</span><span class="o">.</span><span class="n">new</span><span class="p">(</span><span class="n">nums</span><span class="o">.</span><span class="n">length</span><span class="p">,</span><span class="w"> </span><span class="kp">false</span><span class="p">),</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-12-29" id="__codelineno-12-29" name="__codelineno-12-29"></a><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-12-30" id="__codelineno-12-30" name="__codelineno-12-30"></a><span class="k">end</span>
</code></pre></div>
</div>
</div>
</div>
<details class="pythontutor">
<summary>可视化运行</summary>
<p><div style="height: 549px; width: 100%;"><iframe class="pythontutor-iframe" src="https://pythontutor.com/iframe-embed.html#code=def%20backtrack%28%0A%20%20%20%20state%3A%20list%5Bint%5D,%20choices%3A%20list%5Bint%5D,%20selected%3A%20list%5Bbool%5D,%20res%3A%20list%5Blist%5Bint%5D%5D%0A%29%3A%0A%20%20%20%20%22%22%22%E5%9B%9E%E6%BA%AF%E7%AE%97%E6%B3%95%EF%BC%9A%E5%85%A8%E6%8E%92%E5%88%97%20I%22%22%22%0A%20%20%20%20%23%20%E5%BD%93%E7%8A%B6%E6%80%81%E9%95%BF%E5%BA%A6%E7%AD%89%E4%BA%8E%E5%85%83%E7%B4%A0%E6%95%B0%E9%87%8F%E6%97%B6%EF%BC%8C%E8%AE%B0%E5%BD%95%E8%A7%A3%0A%20%20%20%20if%20len%28state%29%20%3D%3D%20len%28choices%29%3A%0A%20%20%20%20%20%20%20%20res.append%28list%28state%29%29%0A%20%20%20%20%20%20%20%20return%0A%20%20%20%20%23%20%E9%81%8D%E5%8E%86%E6%89%80%E6%9C%89%E9%80%89%E6%8B%A9%0A%20%20%20%20for%20i,%20choice%20in%20enumerate%28choices%29%3A%0A%20%20%20%20%20%20%20%20%23%20%E5%89%AA%E6%9E%9D%EF%BC%9A%E4%B8%8D%E5%85%81%E8%AE%B8%E9%87%8D%E5%A4%8D%E9%80%89%E6%8B%A9%E5%85%83%E7%B4%A0%0A%20%20%20%20%20%20%20%20if%20not%20selected%5Bi%5D%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%B0%9D%E8%AF%95%EF%BC%9A%E5%81%9A%E5%87%BA%E9%80%89%E6%8B%A9%EF%BC%8C%E6%9B%B4%E6%96%B0%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20True%0A%20%20%20%20%20%20%20%20%20%20%20%20state.append%28choice%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E8%BF%9B%E8%A1%8C%E4%B8%8B%E4%B8%80%E8%BD%AE%E9%80%89%E6%8B%A9%0A%20%20%20%20%20%20%20%20%20%20%20%20backtrack%28state,%20choices,%20selected,%20res%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%9B%9E%E9%80%80%EF%BC%9A%E6%92%A4%E9%94%80%E9%80%89%E6%8B%A9%EF%BC%8C%E6%81%A2%E5%A4%8D%E5%88%B0%E4%B9%8B%E5%89%8D%E7%9A%84%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20False%0A%20%20%20%20%20%20%20%20%20%20%20%20state.pop%28%29%0A%0A%0Adef%20permutations_i%28nums%3A%20list%5Bint%5D%29%20-%3E%20list%5Blist%5Bint%5D%5D%3A%0A%20%20%20%20%22%22%22%E5%85%A8%E6%8E%92%E5%88%97%20I%22%22%22%0A%20%20%20%20res%20%3D%20%5B%5D%0A%20%20%20%20backtrack%28state%3D%5B%5D,%20choices%3Dnums,%20selected%3D%5BFalse%5D%20*%20len%28nums%29,%20res%3Dres%29%0A%20%20%20%20return%20res%0A%0A%0A%22%22%22Driver%20Code%22%22%22%0Aif%20__name__%20%3D%3D%20%22__main__%22%3A%0A%20%20%20%20nums%20%3D%20%5B1,%202,%203%5D%0A%0A%20%20%20%20res%20%3D%20permutations_i%28nums%29%0A%0A%20%20%20%20print%28f%22%E8%BE%93%E5%85%A5%E6%95%B0%E7%BB%84%20nums%20%3D%20%7Bnums%7D%22%29%0A%20%20%20%20print%28f%22%E6%89%80%E6%9C%89%E6%8E%92%E5%88%97%20res%20%3D%20%7Bres%7D%22%29&amp;codeDivHeight=472&amp;codeDivWidth=350&amp;cumulative=false&amp;curInstr=13&amp;heapPrimitives=nevernest&amp;origin=opt-frontend.js&amp;py=311&amp;rawInputLstJSON=%5B%5D&amp;textReferences=false" title="可视化运行"> </iframe></div>
<div style="margin-top: 5px;"><a href="https://pythontutor.com/iframe-embed.html#code=def%20backtrack%28%0A%20%20%20%20state%3A%20list%5Bint%5D,%20choices%3A%20list%5Bint%5D,%20selected%3A%20list%5Bbool%5D,%20res%3A%20list%5Blist%5Bint%5D%5D%0A%29%3A%0A%20%20%20%20%22%22%22%E5%9B%9E%E6%BA%AF%E7%AE%97%E6%B3%95%EF%BC%9A%E5%85%A8%E6%8E%92%E5%88%97%20I%22%22%22%0A%20%20%20%20%23%20%E5%BD%93%E7%8A%B6%E6%80%81%E9%95%BF%E5%BA%A6%E7%AD%89%E4%BA%8E%E5%85%83%E7%B4%A0%E6%95%B0%E9%87%8F%E6%97%B6%EF%BC%8C%E8%AE%B0%E5%BD%95%E8%A7%A3%0A%20%20%20%20if%20len%28state%29%20%3D%3D%20len%28choices%29%3A%0A%20%20%20%20%20%20%20%20res.append%28list%28state%29%29%0A%20%20%20%20%20%20%20%20return%0A%20%20%20%20%23%20%E9%81%8D%E5%8E%86%E6%89%80%E6%9C%89%E9%80%89%E6%8B%A9%0A%20%20%20%20for%20i,%20choice%20in%20enumerate%28choices%29%3A%0A%20%20%20%20%20%20%20%20%23%20%E5%89%AA%E6%9E%9D%EF%BC%9A%E4%B8%8D%E5%85%81%E8%AE%B8%E9%87%8D%E5%A4%8D%E9%80%89%E6%8B%A9%E5%85%83%E7%B4%A0%0A%20%20%20%20%20%20%20%20if%20not%20selected%5Bi%5D%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%B0%9D%E8%AF%95%EF%BC%9A%E5%81%9A%E5%87%BA%E9%80%89%E6%8B%A9%EF%BC%8C%E6%9B%B4%E6%96%B0%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20True%0A%20%20%20%20%20%20%20%20%20%20%20%20state.append%28choice%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E8%BF%9B%E8%A1%8C%E4%B8%8B%E4%B8%80%E8%BD%AE%E9%80%89%E6%8B%A9%0A%20%20%20%20%20%20%20%20%20%20%20%20backtrack%28state,%20choices,%20selected,%20res%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%9B%9E%E9%80%80%EF%BC%9A%E6%92%A4%E9%94%80%E9%80%89%E6%8B%A9%EF%BC%8C%E6%81%A2%E5%A4%8D%E5%88%B0%E4%B9%8B%E5%89%8D%E7%9A%84%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20False%0A%20%20%20%20%20%20%20%20%20%20%20%20state.pop%28%29%0A%0A%0Adef%20permutations_i%28nums%3A%20list%5Bint%5D%29%20-%3E%20list%5Blist%5Bint%5D%5D%3A%0A%20%20%20%20%22%22%22%E5%85%A8%E6%8E%92%E5%88%97%20I%22%22%22%0A%20%20%20%20res%20%3D%20%5B%5D%0A%20%20%20%20backtrack%28state%3D%5B%5D,%20choices%3Dnums,%20selected%3D%5BFalse%5D%20*%20len%28nums%29,%20res%3Dres%29%0A%20%20%20%20return%20res%0A%0A%0A%22%22%22Driver%20Code%22%22%22%0Aif%20__name__%20%3D%3D%20%22__main__%22%3A%0A%20%20%20%20nums%20%3D%20%5B1,%202,%203%5D%0A%0A%20%20%20%20res%20%3D%20permutations_i%28nums%29%0A%0A%20%20%20%20print%28f%22%E8%BE%93%E5%85%A5%E6%95%B0%E7%BB%84%20nums%20%3D%20%7Bnums%7D%22%29%0A%20%20%20%20print%28f%22%E6%89%80%E6%9C%89%E6%8E%92%E5%88%97%20res%20%3D%20%7Bres%7D%22%29&amp;codeDivHeight=800&amp;codeDivWidth=600&amp;cumulative=false&amp;curInstr=13&amp;heapPrimitives=nevernest&amp;origin=opt-frontend.js&amp;py=311&amp;rawInputLstJSON=%5B%5D&amp;textReferences=false" rel="noopener noreferrer" target="_blank">全屏观看 &gt;</a></div></p>
</details>
<h2 id="1322">13.2.2   考虑相等元素的情况<a class="headerlink" href="#1322" title="Permanent link"></a></h2>
<div class="admonition question">
<p class="admonition-title">Question</p>
<p>输入一个整数数组,<strong>数组中可能包含重复元素</strong>,返回所有不重复的排列。</p>
</div>
<p>假设输入数组为 <span class="arithmatex">\([1, 1, 2]\)</span> 。为了方便区分两个重复元素 <span class="arithmatex">\(1\)</span> ,我们将第二个 <span class="arithmatex">\(1\)</span> 记为 <span class="arithmatex">\(\hat{1}\)</span> 。</p>
<p>如图 13-7 所示,上述方法生成的排列有一半是重复的。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="chapter_backtracking/permutations_problem.assets/permutations_ii.png" data-dark-src="/assets/figure-svg/figures/2fff432744ca8541bf029ad2.json" data-src="/assets/figure-svg/figures/fd103764caaa0e740565fb7e.json" style=";--figure-ratio:960.0/540.0"><object data="/chapter_backtracking/permutations_problem.assets/permutations_ii.svg" data-theme="light" tabindex="-1" type="image/svg+xml">重复排列</object><object data="/chapter_backtracking/permutations_problem.assets/permutations_ii.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">重复排列</object></ha-svg-figure></p>
<p align="center"> 图 13-7   重复排列 </p>
<p>那么如何去除重复的排列呢?最直接地,考虑借助一个哈希集合,直接对排列结果进行去重。然而这样做不够优雅,<strong>因为生成重复排列的搜索分支没有必要,应当提前识别并剪枝</strong>,这样可以进一步提升算法效率。</p>
<h3 id="1_1">1.   相等元素剪枝<a class="headerlink" href="#1_1" title="Permanent link"></a></h3>
<p>观察图 13-8 ,在第一轮中,选择 <span class="arithmatex">\(1\)</span> 或选择 <span class="arithmatex">\(\hat{1}\)</span> 是等价的,在这两个选择之下生成的所有排列都是重复的。因此应该把 <span class="arithmatex">\(\hat{1}\)</span> 剪枝。</p>
<p>同理,在第一轮选择 <span class="arithmatex">\(2\)</span> 之后,第二轮选择中的 <span class="arithmatex">\(1\)</span> 和 <span class="arithmatex">\(\hat{1}\)</span> 也会产生重复分支,因此也应将第二轮的 <span class="arithmatex">\(\hat{1}\)</span> 剪枝。</p>
<p>从本质上看,<strong>我们的目标是在某一轮选择中,保证多个相等的元素仅被选择一次</strong>。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="chapter_backtracking/permutations_problem.assets/permutations_ii_pruning.png" data-dark-src="/assets/figure-svg/figures/106dfcabd52534b86c100d34.json" data-src="/assets/figure-svg/figures/a35379ca40bbb1e10172ffe9.json" style=";--figure-ratio:960.0/540.0"><object data="/chapter_backtracking/permutations_problem.assets/permutations_ii_pruning.svg" data-theme="light" tabindex="-1" type="image/svg+xml">重复排列剪枝</object><object data="/chapter_backtracking/permutations_problem.assets/permutations_ii_pruning.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">重复排列剪枝</object></ha-svg-figure></p>
<p align="center"> 图 13-8   重复排列剪枝 </p>
<h3 id="2_1">2.   代码实现<a class="headerlink" href="#2_1" title="Permanent link"></a></h3>
<p>在上一题的代码的基础上,我们考虑在每一轮选择中开启一个哈希集合 <code>duplicated</code> ,用于记录该轮中已经尝试过的元素,并将重复元素剪枝:</p>
<div class="tabbed-set tabbed-alternate" data-tabs="2:13"><input checked="checked" id="__tabbed_2_1" name="__tabbed_2" type="radio"/><input id="__tabbed_2_2" name="__tabbed_2" type="radio"/><input id="__tabbed_2_3" name="__tabbed_2" type="radio"/><input id="__tabbed_2_4" name="__tabbed_2" type="radio"/><input id="__tabbed_2_5" name="__tabbed_2" type="radio"/><input id="__tabbed_2_6" name="__tabbed_2" type="radio"/><input id="__tabbed_2_7" name="__tabbed_2" type="radio"/><input id="__tabbed_2_8" name="__tabbed_2" type="radio"/><input id="__tabbed_2_9" name="__tabbed_2" type="radio"/><input id="__tabbed_2_10" name="__tabbed_2" type="radio"/><input id="__tabbed_2_11" name="__tabbed_2" type="radio"/><input id="__tabbed_2_12" name="__tabbed_2" type="radio"/><input id="__tabbed_2_13" name="__tabbed_2" type="radio"/><div class="tabbed-labels"><label for="__tabbed_2_1">Python</label><label for="__tabbed_2_2">C++</label><label for="__tabbed_2_3">Java</label><label for="__tabbed_2_4">C#</label><label for="__tabbed_2_5">Go</label><label for="__tabbed_2_6">Swift</label><label for="__tabbed_2_7">JS</label><label for="__tabbed_2_8">TS</label><label for="__tabbed_2_9">Dart</label><label for="__tabbed_2_10">Rust</label><label for="__tabbed_2_11">C</label><label for="__tabbed_2_12">Kotlin</label><label for="__tabbed_2_13">Ruby</label></div>
<div class="tabbed-content">
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.py</span><pre><span></span><code><a href="#__codelineno-13-1" id="__codelineno-13-1" name="__codelineno-13-1"></a><span class="k">def</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span>
<a href="#__codelineno-13-2" id="__codelineno-13-2" name="__codelineno-13-2"></a> <span class="n">state</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">choices</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">selected</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">bool</span><span class="p">],</span> <span class="n">res</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">]]</span>
<a href="#__codelineno-13-3" id="__codelineno-13-3" name="__codelineno-13-3"></a><span class="p">):</span>
<a href="#__codelineno-13-4" id="__codelineno-13-4" name="__codelineno-13-4"></a><span class="w"> </span><span class="sd">"""回溯算法:全排列 II"""</span>
<a href="#__codelineno-13-5" id="__codelineno-13-5" name="__codelineno-13-5"></a> <span class="c1"># 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-13-6" id="__codelineno-13-6" name="__codelineno-13-6"></a> <span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">state</span><span class="p">)</span> <span class="o">==</span> <span class="nb">len</span><span class="p">(</span><span class="n">choices</span><span class="p">):</span>
<a href="#__codelineno-13-7" id="__codelineno-13-7" name="__codelineno-13-7"></a> <span class="n">res</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="nb">list</span><span class="p">(</span><span class="n">state</span><span class="p">))</span>
<a href="#__codelineno-13-8" id="__codelineno-13-8" name="__codelineno-13-8"></a> <span class="k">return</span>
<a href="#__codelineno-13-9" id="__codelineno-13-9" name="__codelineno-13-9"></a> <span class="c1"># 遍历所有选择</span>
<a href="#__codelineno-13-10" id="__codelineno-13-10" name="__codelineno-13-10"></a> <span class="n">duplicated</span> <span class="o">=</span> <span class="nb">set</span><span class="p">[</span><span class="nb">int</span><span class="p">]()</span>
<a href="#__codelineno-13-11" id="__codelineno-13-11" name="__codelineno-13-11"></a> <span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">choice</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="n">choices</span><span class="p">):</span>
<a href="#__codelineno-13-12" id="__codelineno-13-12" name="__codelineno-13-12"></a> <span class="c1"># 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-13-13" id="__codelineno-13-13" name="__codelineno-13-13"></a> <span class="k">if</span> <span class="ow">not</span> <span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="ow">and</span> <span class="n">choice</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">duplicated</span><span class="p">:</span>
<a href="#__codelineno-13-14" id="__codelineno-13-14" name="__codelineno-13-14"></a> <span class="c1"># 尝试:做出选择,更新状态</span>
<a href="#__codelineno-13-15" id="__codelineno-13-15" name="__codelineno-13-15"></a> <span class="n">duplicated</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span> <span class="c1"># 记录选择过的元素值</span>
<a href="#__codelineno-13-16" id="__codelineno-13-16" name="__codelineno-13-16"></a> <span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="kc">True</span>
<a href="#__codelineno-13-17" id="__codelineno-13-17" name="__codelineno-13-17"></a> <span class="n">state</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-13-18" id="__codelineno-13-18" name="__codelineno-13-18"></a> <span class="c1"># 进行下一轮选择</span>
<a href="#__codelineno-13-19" id="__codelineno-13-19" name="__codelineno-13-19"></a> <span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span> <span class="n">choices</span><span class="p">,</span> <span class="n">selected</span><span class="p">,</span> <span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-13-20" id="__codelineno-13-20" name="__codelineno-13-20"></a> <span class="c1"># 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-13-21" id="__codelineno-13-21" name="__codelineno-13-21"></a> <span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="kc">False</span>
<a href="#__codelineno-13-22" id="__codelineno-13-22" name="__codelineno-13-22"></a> <span class="n">state</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<a href="#__codelineno-13-23" id="__codelineno-13-23" name="__codelineno-13-23"></a>
<a href="#__codelineno-13-24" id="__codelineno-13-24" name="__codelineno-13-24"></a><span class="k">def</span><span class="w"> </span><span class="nf">permutations_ii</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">])</span> <span class="o">-&gt;</span> <span class="nb">list</span><span class="p">[</span><span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">]]:</span>
<a href="#__codelineno-13-25" id="__codelineno-13-25" name="__codelineno-13-25"></a><span class="w"> </span><span class="sd">"""全排列 II"""</span>
<a href="#__codelineno-13-26" id="__codelineno-13-26" name="__codelineno-13-26"></a> <span class="n">res</span> <span class="o">=</span> <span class="p">[]</span>
<a href="#__codelineno-13-27" id="__codelineno-13-27" name="__codelineno-13-27"></a> <span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="o">=</span><span class="p">[],</span> <span class="n">choices</span><span class="o">=</span><span class="n">nums</span><span class="p">,</span> <span class="n">selected</span><span class="o">=</span><span class="p">[</span><span class="kc">False</span><span class="p">]</span> <span class="o">*</span> <span class="nb">len</span><span class="p">(</span><span class="n">nums</span><span class="p">),</span> <span class="n">res</span><span class="o">=</span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-13-28" id="__codelineno-13-28" name="__codelineno-13-28"></a> <span class="k">return</span> <span class="n">res</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.cpp</span><pre><span></span><code><a href="#__codelineno-14-1" id="__codelineno-14-1" name="__codelineno-14-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-14-2" id="__codelineno-14-2" name="__codelineno-14-2"></a><span class="kt">void</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">bool</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-14-3" id="__codelineno-14-3" name="__codelineno-14-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-14-4" id="__codelineno-14-4" name="__codelineno-14-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">size</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">size</span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-14-5" id="__codelineno-14-5" name="__codelineno-14-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<a href="#__codelineno-14-6" id="__codelineno-14-6" name="__codelineno-14-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-14-7" id="__codelineno-14-7" name="__codelineno-14-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-14-8" id="__codelineno-14-8" name="__codelineno-14-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-14-9" id="__codelineno-14-9" name="__codelineno-14-9"></a><span class="w"> </span><span class="n">unordered_set</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">duplicated</span><span class="p">;</span>
<a href="#__codelineno-14-10" id="__codelineno-14-10" name="__codelineno-14-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">size</span><span class="p">();</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-14-11" id="__codelineno-14-11" name="__codelineno-14-11"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-14-12" id="__codelineno-14-12" name="__codelineno-14-12"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-14-13" id="__codelineno-14-13" name="__codelineno-14-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="n">find</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="n">end</span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-14-14" id="__codelineno-14-14" name="__codelineno-14-14"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-14-15" id="__codelineno-14-15" name="__codelineno-14-15"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="n">emplace</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-14-16" id="__codelineno-14-16" name="__codelineno-14-16"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<a href="#__codelineno-14-17" id="__codelineno-14-17" name="__codelineno-14-17"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-14-18" id="__codelineno-14-18" name="__codelineno-14-18"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-14-19" id="__codelineno-14-19" name="__codelineno-14-19"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-14-20" id="__codelineno-14-20" name="__codelineno-14-20"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-14-21" id="__codelineno-14-21" name="__codelineno-14-21"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<a href="#__codelineno-14-22" id="__codelineno-14-22" name="__codelineno-14-22"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">pop_back</span><span class="p">();</span>
<a href="#__codelineno-14-23" id="__codelineno-14-23" name="__codelineno-14-23"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-14-24" id="__codelineno-14-24" name="__codelineno-14-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-14-25" id="__codelineno-14-25" name="__codelineno-14-25"></a><span class="p">}</span>
<a href="#__codelineno-14-26" id="__codelineno-14-26" name="__codelineno-14-26"></a>
<a href="#__codelineno-14-27" id="__codelineno-14-27" name="__codelineno-14-27"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-14-28" id="__codelineno-14-28" name="__codelineno-14-28"></a><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">permutationsII</span><span class="p">(</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-14-29" id="__codelineno-14-29" name="__codelineno-14-29"></a><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">;</span>
<a href="#__codelineno-14-30" id="__codelineno-14-30" name="__codelineno-14-30"></a><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">bool</span><span class="o">&gt;</span><span class="w"> </span><span class="n">selected</span><span class="p">(</span><span class="n">nums</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span><span class="w"> </span><span class="nb">false</span><span class="p">);</span>
<a href="#__codelineno-14-31" id="__codelineno-14-31" name="__codelineno-14-31"></a><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-14-32" id="__codelineno-14-32" name="__codelineno-14-32"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-14-33" id="__codelineno-14-33" name="__codelineno-14-33"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-14-34" id="__codelineno-14-34" name="__codelineno-14-34"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.java</span><pre><span></span><code><a href="#__codelineno-15-1" id="__codelineno-15-1" name="__codelineno-15-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-15-2" id="__codelineno-15-2" name="__codelineno-15-2"></a><span class="kt">void</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">[]</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-15-3" id="__codelineno-15-3" name="__codelineno-15-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-15-4" id="__codelineno-15-4" name="__codelineno-15-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-15-5" id="__codelineno-15-5" name="__codelineno-15-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="p">(</span><span class="n">state</span><span class="p">));</span>
<a href="#__codelineno-15-6" id="__codelineno-15-6" name="__codelineno-15-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-15-7" id="__codelineno-15-7" name="__codelineno-15-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-15-8" id="__codelineno-15-8" name="__codelineno-15-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-15-9" id="__codelineno-15-9" name="__codelineno-15-9"></a><span class="w"> </span><span class="n">Set</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">HashSet</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="p">();</span>
<a href="#__codelineno-15-10" id="__codelineno-15-10" name="__codelineno-15-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">length</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-15-11" id="__codelineno-15-11" name="__codelineno-15-11"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="p">;</span>
<a href="#__codelineno-15-12" id="__codelineno-15-12" name="__codelineno-15-12"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-15-13" id="__codelineno-15-13" name="__codelineno-15-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">.</span><span class="na">contains</span><span class="p">(</span><span class="n">choice</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-15-14" id="__codelineno-15-14" name="__codelineno-15-14"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-15-15" id="__codelineno-15-15" name="__codelineno-15-15"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-15-16" id="__codelineno-15-16" name="__codelineno-15-16"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-15-17" id="__codelineno-15-17" name="__codelineno-15-17"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-15-18" id="__codelineno-15-18" name="__codelineno-15-18"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-15-19" id="__codelineno-15-19" name="__codelineno-15-19"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-15-20" id="__codelineno-15-20" name="__codelineno-15-20"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-15-21" id="__codelineno-15-21" name="__codelineno-15-21"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-15-22" id="__codelineno-15-22" name="__codelineno-15-22"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">remove</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="p">()</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
<a href="#__codelineno-15-23" id="__codelineno-15-23" name="__codelineno-15-23"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-15-24" id="__codelineno-15-24" name="__codelineno-15-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-15-25" id="__codelineno-15-25" name="__codelineno-15-25"></a><span class="p">}</span>
<a href="#__codelineno-15-26" id="__codelineno-15-26" name="__codelineno-15-26"></a>
<a href="#__codelineno-15-27" id="__codelineno-15-27" name="__codelineno-15-27"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-15-28" id="__codelineno-15-28" name="__codelineno-15-28"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="nf">permutationsII</span><span class="p">(</span><span class="kt">int</span><span class="o">[]</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-15-29" id="__codelineno-15-29" name="__codelineno-15-29"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;&gt;</span><span class="p">();</span>
<a href="#__codelineno-15-30" id="__codelineno-15-30" name="__codelineno-15-30"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="p">(),</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">boolean</span><span class="o">[</span><span class="n">nums</span><span class="p">.</span><span class="na">length</span><span class="o">]</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-15-31" id="__codelineno-15-31" name="__codelineno-15-31"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-15-32" id="__codelineno-15-32" name="__codelineno-15-32"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.cs</span><pre><span></span><code><a href="#__codelineno-16-1" id="__codelineno-16-1" name="__codelineno-16-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-16-2" id="__codelineno-16-2" name="__codelineno-16-2"></a><span class="k">void</span><span class="w"> </span><span class="nf">Backtrack</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="p">[]</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-16-3" id="__codelineno-16-3" name="__codelineno-16-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-16-4" id="__codelineno-16-4" name="__codelineno-16-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">Count</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">Length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-16-5" id="__codelineno-16-5" name="__codelineno-16-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="p">(</span><span class="n">state</span><span class="p">));</span>
<a href="#__codelineno-16-6" id="__codelineno-16-6" name="__codelineno-16-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-16-7" id="__codelineno-16-7" name="__codelineno-16-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-16-8" id="__codelineno-16-8" name="__codelineno-16-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-16-9" id="__codelineno-16-9" name="__codelineno-16-9"></a><span class="w"> </span><span class="n">HashSet</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-16-10" id="__codelineno-16-10" name="__codelineno-16-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">Length</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-16-11" id="__codelineno-16-11" name="__codelineno-16-11"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-16-12" id="__codelineno-16-12" name="__codelineno-16-12"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-16-13" id="__codelineno-16-13" name="__codelineno-16-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">.</span><span class="n">Contains</span><span class="p">(</span><span class="n">choice</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-16-14" id="__codelineno-16-14" name="__codelineno-16-14"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-16-15" id="__codelineno-16-15" name="__codelineno-16-15"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-16-16" id="__codelineno-16-16" name="__codelineno-16-16"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">true</span><span class="p">;</span>
<a href="#__codelineno-16-17" id="__codelineno-16-17" name="__codelineno-16-17"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-16-18" id="__codelineno-16-18" name="__codelineno-16-18"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-16-19" id="__codelineno-16-19" name="__codelineno-16-19"></a><span class="w"> </span><span class="n">Backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-16-20" id="__codelineno-16-20" name="__codelineno-16-20"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-16-21" id="__codelineno-16-21" name="__codelineno-16-21"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">false</span><span class="p">;</span>
<a href="#__codelineno-16-22" id="__codelineno-16-22" name="__codelineno-16-22"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">RemoveAt</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">Count</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
<a href="#__codelineno-16-23" id="__codelineno-16-23" name="__codelineno-16-23"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-16-24" id="__codelineno-16-24" name="__codelineno-16-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-16-25" id="__codelineno-16-25" name="__codelineno-16-25"></a><span class="p">}</span>
<a href="#__codelineno-16-26" id="__codelineno-16-26" name="__codelineno-16-26"></a>
<a href="#__codelineno-16-27" id="__codelineno-16-27" name="__codelineno-16-27"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-16-28" id="__codelineno-16-28" name="__codelineno-16-28"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">PermutationsII</span><span class="p">(</span><span class="kt">int</span><span class="p">[]</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-16-29" id="__codelineno-16-29" name="__codelineno-16-29"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-16-30" id="__codelineno-16-30" name="__codelineno-16-30"></a><span class="w"> </span><span class="n">Backtrack</span><span class="p">([],</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="kt">bool</span><span class="p">[</span><span class="n">nums</span><span class="p">.</span><span class="n">Length</span><span class="p">],</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-16-31" id="__codelineno-16-31" name="__codelineno-16-31"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-16-32" id="__codelineno-16-32" name="__codelineno-16-32"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.go</span><pre><span></span><code><a href="#__codelineno-17-1" id="__codelineno-17-1" name="__codelineno-17-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-17-2" id="__codelineno-17-2" name="__codelineno-17-2"></a><span class="kd">func</span><span class="w"> </span><span class="nx">backtrackII</span><span class="p">(</span><span class="nx">state</span><span class="w"> </span><span class="o">*</span><span class="p">[]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="w"> </span><span class="o">*</span><span class="p">[]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="w"> </span><span class="o">*</span><span class="p">[]</span><span class="kt">bool</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="w"> </span><span class="o">*</span><span class="p">[][]</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-17-3" id="__codelineno-17-3" name="__codelineno-17-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-17-4" id="__codelineno-17-4" name="__codelineno-17-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">choices</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-17-5" id="__codelineno-17-5" name="__codelineno-17-5"></a><span class="w"> </span><span class="nx">newState</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">append</span><span class="p">([]</span><span class="kt">int</span><span class="p">{},</span><span class="w"> </span><span class="o">*</span><span class="nx">state</span><span class="p">...)</span>
<a href="#__codelineno-17-6" id="__codelineno-17-6" name="__codelineno-17-6"></a><span class="w"> </span><span class="o">*</span><span class="nx">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">append</span><span class="p">(</span><span class="o">*</span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">newState</span><span class="p">)</span>
<a href="#__codelineno-17-7" id="__codelineno-17-7" name="__codelineno-17-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-17-8" id="__codelineno-17-8" name="__codelineno-17-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-17-9" id="__codelineno-17-9" name="__codelineno-17-9"></a><span class="w"> </span><span class="nx">duplicated</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">(</span><span class="kt">map</span><span class="p">[</span><span class="kt">int</span><span class="p">]</span><span class="kd">struct</span><span class="p">{},</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
<a href="#__codelineno-17-10" id="__codelineno-17-10" name="__codelineno-17-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">choices</span><span class="p">);</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-17-11" id="__codelineno-17-11" name="__codelineno-17-11"></a><span class="w"> </span><span class="nx">choice</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">choices</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span>
<a href="#__codelineno-17-12" id="__codelineno-17-12" name="__codelineno-17-12"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-17-13" id="__codelineno-17-13" name="__codelineno-17-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">ok</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">duplicated</span><span class="p">[</span><span class="nx">choice</span><span class="p">];</span><span class="w"> </span><span class="o">!</span><span class="nx">ok</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="p">(</span><span class="o">*</span><span class="nx">selected</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-17-14" id="__codelineno-17-14" name="__codelineno-17-14"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-17-15" id="__codelineno-17-15" name="__codelineno-17-15"></a><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-17-16" id="__codelineno-17-16" name="__codelineno-17-16"></a><span class="w"> </span><span class="nx">duplicated</span><span class="p">[</span><span class="nx">choice</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kd">struct</span><span class="p">{}{}</span>
<a href="#__codelineno-17-17" id="__codelineno-17-17" name="__codelineno-17-17"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">selected</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-17-18" id="__codelineno-17-18" name="__codelineno-17-18"></a><span class="w"> </span><span class="o">*</span><span class="nx">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">append</span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choice</span><span class="p">)</span>
<a href="#__codelineno-17-19" id="__codelineno-17-19" name="__codelineno-17-19"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-17-20" id="__codelineno-17-20" name="__codelineno-17-20"></a><span class="w"> </span><span class="nx">backtrackII</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">)</span>
<a href="#__codelineno-17-21" id="__codelineno-17-21" name="__codelineno-17-21"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-17-22" id="__codelineno-17-22" name="__codelineno-17-22"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">selected</span><span class="p">)[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-17-23" id="__codelineno-17-23" name="__codelineno-17-23"></a><span class="w"> </span><span class="o">*</span><span class="nx">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)[:</span><span class="nb">len</span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
<a href="#__codelineno-17-24" id="__codelineno-17-24" name="__codelineno-17-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-17-25" id="__codelineno-17-25" name="__codelineno-17-25"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-17-26" id="__codelineno-17-26" name="__codelineno-17-26"></a><span class="p">}</span>
<a href="#__codelineno-17-27" id="__codelineno-17-27" name="__codelineno-17-27"></a>
<a href="#__codelineno-17-28" id="__codelineno-17-28" name="__codelineno-17-28"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-17-29" id="__codelineno-17-29" name="__codelineno-17-29"></a><span class="kd">func</span><span class="w"> </span><span class="nx">permutationsII</span><span class="p">(</span><span class="nx">nums</span><span class="w"> </span><span class="p">[]</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="p">[][]</span><span class="kt">int</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-17-30" id="__codelineno-17-30" name="__codelineno-17-30"></a><span class="w"> </span><span class="nx">res</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">([][]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
<a href="#__codelineno-17-31" id="__codelineno-17-31" name="__codelineno-17-31"></a><span class="w"> </span><span class="nx">state</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">([]</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
<a href="#__codelineno-17-32" id="__codelineno-17-32" name="__codelineno-17-32"></a><span class="w"> </span><span class="nx">selected</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">([]</span><span class="kt">bool</span><span class="p">,</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="nx">nums</span><span class="p">))</span>
<a href="#__codelineno-17-33" id="__codelineno-17-33" name="__codelineno-17-33"></a><span class="w"> </span><span class="nx">backtrackII</span><span class="p">(</span><span class="o">&amp;</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">nums</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">res</span><span class="p">)</span>
<a href="#__codelineno-17-34" id="__codelineno-17-34" name="__codelineno-17-34"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span>
<a href="#__codelineno-17-35" id="__codelineno-17-35" name="__codelineno-17-35"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.swift</span><pre><span></span><code><a href="#__codelineno-18-1" id="__codelineno-18-1" name="__codelineno-18-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-18-2" id="__codelineno-18-2" name="__codelineno-18-2"></a><span class="kd">func</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="kr">inout</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">],</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">],</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="kr">inout</span><span class="w"> </span><span class="p">[</span><span class="nb">Bool</span><span class="p">],</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="kr">inout</span><span class="w"> </span><span class="p">[[</span><span class="nb">Int</span><span class="p">]])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-18-3" id="__codelineno-18-3" name="__codelineno-18-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-18-4" id="__codelineno-18-4" name="__codelineno-18-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="bp">count</span><span class="w"> </span><span class="p">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="bp">count</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-18-5" id="__codelineno-18-5" name="__codelineno-18-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">state</span><span class="p">)</span>
<a href="#__codelineno-18-6" id="__codelineno-18-6" name="__codelineno-18-6"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-18-7" id="__codelineno-18-7" name="__codelineno-18-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-18-8" id="__codelineno-18-8" name="__codelineno-18-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-18-9" id="__codelineno-18-9" name="__codelineno-18-9"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">duplicated</span><span class="p">:</span><span class="w"> </span><span class="n">Set</span><span class="p">&lt;</span><span class="nb">Int</span><span class="p">&gt;</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[]</span>
<a href="#__codelineno-18-10" id="__codelineno-18-10" name="__codelineno-18-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">enumerated</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-18-11" id="__codelineno-18-11" name="__codelineno-18-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-18-12" id="__codelineno-18-12" name="__codelineno-18-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">],</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">.</span><span class="bp">contains</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-18-13" id="__codelineno-18-13" name="__codelineno-18-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-18-14" id="__codelineno-18-14" name="__codelineno-18-14"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="bp">insert</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-18-15" id="__codelineno-18-15" name="__codelineno-18-15"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-18-16" id="__codelineno-18-16" name="__codelineno-18-16"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-18-17" id="__codelineno-18-17" name="__codelineno-18-17"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-18-18" id="__codelineno-18-18" name="__codelineno-18-18"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-18-19" id="__codelineno-18-19" name="__codelineno-18-19"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-18-20" id="__codelineno-18-20" name="__codelineno-18-20"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-18-21" id="__codelineno-18-21" name="__codelineno-18-21"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="bp">removeLast</span><span class="p">()</span>
<a href="#__codelineno-18-22" id="__codelineno-18-22" name="__codelineno-18-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-18-23" id="__codelineno-18-23" name="__codelineno-18-23"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-18-24" id="__codelineno-18-24" name="__codelineno-18-24"></a><span class="p">}</span>
<a href="#__codelineno-18-25" id="__codelineno-18-25" name="__codelineno-18-25"></a>
<a href="#__codelineno-18-26" id="__codelineno-18-26" name="__codelineno-18-26"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-18-27" id="__codelineno-18-27" name="__codelineno-18-27"></a><span class="kd">func</span><span class="w"> </span><span class="nf">permutationsII</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">])</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">[[</span><span class="nb">Int</span><span class="p">]]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-18-28" id="__codelineno-18-28" name="__codelineno-18-28"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">state</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="nb">Int</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[]</span>
<a href="#__codelineno-18-29" id="__codelineno-18-29" name="__codelineno-18-29"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">selected</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w"> </span><span class="bp">count</span><span class="p">:</span><span class="w"> </span><span class="n">nums</span><span class="p">.</span><span class="bp">count</span><span class="p">)</span>
<a href="#__codelineno-18-30" id="__codelineno-18-30" name="__codelineno-18-30"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">res</span><span class="p">:</span><span class="w"> </span><span class="p">[[</span><span class="nb">Int</span><span class="p">]]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[]</span>
<a href="#__codelineno-18-31" id="__codelineno-18-31" name="__codelineno-18-31"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-18-32" id="__codelineno-18-32" name="__codelineno-18-32"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-18-33" id="__codelineno-18-33" name="__codelineno-18-33"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.js</span><pre><span></span><code><a href="#__codelineno-19-1" id="__codelineno-19-1" name="__codelineno-19-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-19-2" id="__codelineno-19-2" name="__codelineno-19-2"></a><span class="kd">function</span><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-19-3" id="__codelineno-19-3" name="__codelineno-19-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-19-4" id="__codelineno-19-4" name="__codelineno-19-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">state</span><span class="p">.</span><span class="nx">length</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-19-5" id="__codelineno-19-5" name="__codelineno-19-5"></a><span class="w"> </span><span class="nx">res</span><span class="p">.</span><span class="nx">push</span><span class="p">([...</span><span class="nx">state</span><span class="p">]);</span>
<a href="#__codelineno-19-6" id="__codelineno-19-6" name="__codelineno-19-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-19-7" id="__codelineno-19-7" name="__codelineno-19-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-19-8" id="__codelineno-19-8" name="__codelineno-19-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-19-9" id="__codelineno-19-9" name="__codelineno-19-9"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ow">new</span><span class="w"> </span><span class="nb">Set</span><span class="p">();</span>
<a href="#__codelineno-19-10" id="__codelineno-19-10" name="__codelineno-19-10"></a><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">forEach</span><span class="p">((</span><span class="nx">choice</span><span class="p">,</span><span class="w"> </span><span class="nx">i</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-19-11" id="__codelineno-19-11" name="__codelineno-19-11"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-19-12" id="__codelineno-19-12" name="__codelineno-19-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="nx">duplicated</span><span class="p">.</span><span class="nx">has</span><span class="p">(</span><span class="nx">choice</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-19-13" id="__codelineno-19-13" name="__codelineno-19-13"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-19-14" id="__codelineno-19-14" name="__codelineno-19-14"></a><span class="w"> </span><span class="nx">duplicated</span><span class="p">.</span><span class="nx">add</span><span class="p">(</span><span class="nx">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-19-15" id="__codelineno-19-15" name="__codelineno-19-15"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-19-16" id="__codelineno-19-16" name="__codelineno-19-16"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">choice</span><span class="p">);</span>
<a href="#__codelineno-19-17" id="__codelineno-19-17" name="__codelineno-19-17"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-19-18" id="__codelineno-19-18" name="__codelineno-19-18"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-19-19" id="__codelineno-19-19" name="__codelineno-19-19"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-19-20" id="__codelineno-19-20" name="__codelineno-19-20"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-19-21" id="__codelineno-19-21" name="__codelineno-19-21"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">pop</span><span class="p">();</span>
<a href="#__codelineno-19-22" id="__codelineno-19-22" name="__codelineno-19-22"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-19-23" id="__codelineno-19-23" name="__codelineno-19-23"></a><span class="w"> </span><span class="p">});</span>
<a href="#__codelineno-19-24" id="__codelineno-19-24" name="__codelineno-19-24"></a><span class="p">}</span>
<a href="#__codelineno-19-25" id="__codelineno-19-25" name="__codelineno-19-25"></a>
<a href="#__codelineno-19-26" id="__codelineno-19-26" name="__codelineno-19-26"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-19-27" id="__codelineno-19-27" name="__codelineno-19-27"></a><span class="kd">function</span><span class="w"> </span><span class="nx">permutationsII</span><span class="p">(</span><span class="nx">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-19-28" id="__codelineno-19-28" name="__codelineno-19-28"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-19-29" id="__codelineno-19-29" name="__codelineno-19-29"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">([],</span><span class="w"> </span><span class="nx">nums</span><span class="p">,</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">nums</span><span class="p">.</span><span class="nx">length</span><span class="p">).</span><span class="nx">fill</span><span class="p">(</span><span class="kc">false</span><span class="p">),</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-19-30" id="__codelineno-19-30" name="__codelineno-19-30"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span><span class="p">;</span>
<a href="#__codelineno-19-31" id="__codelineno-19-31" name="__codelineno-19-31"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.ts</span><pre><span></span><code><a href="#__codelineno-20-1" id="__codelineno-20-1" name="__codelineno-20-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-20-2" id="__codelineno-20-2" name="__codelineno-20-2"></a><span class="kd">function</span><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span>
<a href="#__codelineno-20-3" id="__codelineno-20-3" name="__codelineno-20-3"></a><span class="w"> </span><span class="nx">state</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span>
<a href="#__codelineno-20-4" id="__codelineno-20-4" name="__codelineno-20-4"></a><span class="w"> </span><span class="nx">choices</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span>
<a href="#__codelineno-20-5" id="__codelineno-20-5" name="__codelineno-20-5"></a><span class="w"> </span><span class="nx">selected</span><span class="o">:</span><span class="w"> </span><span class="kt">boolean</span><span class="p">[],</span>
<a href="#__codelineno-20-6" id="__codelineno-20-6" name="__codelineno-20-6"></a><span class="w"> </span><span class="nx">res</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[][]</span>
<a href="#__codelineno-20-7" id="__codelineno-20-7" name="__codelineno-20-7"></a><span class="p">)</span><span class="o">:</span><span class="w"> </span><span class="ow">void</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-20-8" id="__codelineno-20-8" name="__codelineno-20-8"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-20-9" id="__codelineno-20-9" name="__codelineno-20-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">state</span><span class="p">.</span><span class="nx">length</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-20-10" id="__codelineno-20-10" name="__codelineno-20-10"></a><span class="w"> </span><span class="nx">res</span><span class="p">.</span><span class="nx">push</span><span class="p">([...</span><span class="nx">state</span><span class="p">]);</span>
<a href="#__codelineno-20-11" id="__codelineno-20-11" name="__codelineno-20-11"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-20-12" id="__codelineno-20-12" name="__codelineno-20-12"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-20-13" id="__codelineno-20-13" name="__codelineno-20-13"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-20-14" id="__codelineno-20-14" name="__codelineno-20-14"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ow">new</span><span class="w"> </span><span class="nb">Set</span><span class="p">();</span>
<a href="#__codelineno-20-15" id="__codelineno-20-15" name="__codelineno-20-15"></a><span class="w"> </span><span class="nx">choices</span><span class="p">.</span><span class="nx">forEach</span><span class="p">((</span><span class="nx">choice</span><span class="p">,</span><span class="w"> </span><span class="nx">i</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-20-16" id="__codelineno-20-16" name="__codelineno-20-16"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-20-17" id="__codelineno-20-17" name="__codelineno-20-17"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="nx">duplicated</span><span class="p">.</span><span class="nx">has</span><span class="p">(</span><span class="nx">choice</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-20-18" id="__codelineno-20-18" name="__codelineno-20-18"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-20-19" id="__codelineno-20-19" name="__codelineno-20-19"></a><span class="w"> </span><span class="nx">duplicated</span><span class="p">.</span><span class="nx">add</span><span class="p">(</span><span class="nx">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-20-20" id="__codelineno-20-20" name="__codelineno-20-20"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-20-21" id="__codelineno-20-21" name="__codelineno-20-21"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">choice</span><span class="p">);</span>
<a href="#__codelineno-20-22" id="__codelineno-20-22" name="__codelineno-20-22"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-20-23" id="__codelineno-20-23" name="__codelineno-20-23"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">choices</span><span class="p">,</span><span class="w"> </span><span class="nx">selected</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-20-24" id="__codelineno-20-24" name="__codelineno-20-24"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-20-25" id="__codelineno-20-25" name="__codelineno-20-25"></a><span class="w"> </span><span class="nx">selected</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-20-26" id="__codelineno-20-26" name="__codelineno-20-26"></a><span class="w"> </span><span class="nx">state</span><span class="p">.</span><span class="nx">pop</span><span class="p">();</span>
<a href="#__codelineno-20-27" id="__codelineno-20-27" name="__codelineno-20-27"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-20-28" id="__codelineno-20-28" name="__codelineno-20-28"></a><span class="w"> </span><span class="p">});</span>
<a href="#__codelineno-20-29" id="__codelineno-20-29" name="__codelineno-20-29"></a><span class="p">}</span>
<a href="#__codelineno-20-30" id="__codelineno-20-30" name="__codelineno-20-30"></a>
<a href="#__codelineno-20-31" id="__codelineno-20-31" name="__codelineno-20-31"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-20-32" id="__codelineno-20-32" name="__codelineno-20-32"></a><span class="kd">function</span><span class="w"> </span><span class="nx">permutationsII</span><span class="p">(</span><span class="nx">nums</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[])</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[][]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-20-33" id="__codelineno-20-33" name="__codelineno-20-33"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">res</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[][]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-20-34" id="__codelineno-20-34" name="__codelineno-20-34"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">([],</span><span class="w"> </span><span class="nx">nums</span><span class="p">,</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">nums</span><span class="p">.</span><span class="nx">length</span><span class="p">).</span><span class="nx">fill</span><span class="p">(</span><span class="kc">false</span><span class="p">),</span><span class="w"> </span><span class="nx">res</span><span class="p">);</span>
<a href="#__codelineno-20-35" id="__codelineno-20-35" name="__codelineno-20-35"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span><span class="p">;</span>
<a href="#__codelineno-20-36" id="__codelineno-20-36" name="__codelineno-20-36"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.dart</span><pre><span></span><code><a href="#__codelineno-21-1" id="__codelineno-21-1" name="__codelineno-21-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-21-2" id="__codelineno-21-2" name="__codelineno-21-2"></a><span class="kt">void</span><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span>
<a href="#__codelineno-21-3" id="__codelineno-21-3" name="__codelineno-21-3"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">,</span>
<a href="#__codelineno-21-4" id="__codelineno-21-4" name="__codelineno-21-4"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span>
<a href="#__codelineno-21-5" id="__codelineno-21-5" name="__codelineno-21-5"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">bool</span><span class="o">&gt;</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span>
<a href="#__codelineno-21-6" id="__codelineno-21-6" name="__codelineno-21-6"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">,</span>
<a href="#__codelineno-21-7" id="__codelineno-21-7" name="__codelineno-21-7"></a><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-21-8" id="__codelineno-21-8" name="__codelineno-21-8"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-21-9" id="__codelineno-21-9" name="__codelineno-21-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">length</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">length</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-21-10" id="__codelineno-21-10" name="__codelineno-21-10"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">List</span><span class="p">.</span><span class="n">from</span><span class="p">(</span><span class="n">state</span><span class="p">));</span>
<a href="#__codelineno-21-11" id="__codelineno-21-11" name="__codelineno-21-11"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-21-12" id="__codelineno-21-12" name="__codelineno-21-12"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-21-13" id="__codelineno-21-13" name="__codelineno-21-13"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-21-14" id="__codelineno-21-14" name="__codelineno-21-14"></a><span class="w"> </span><span class="n">Set</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{};</span>
<a href="#__codelineno-21-15" id="__codelineno-21-15" name="__codelineno-21-15"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">length</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-21-16" id="__codelineno-21-16" name="__codelineno-21-16"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-21-17" id="__codelineno-21-17" name="__codelineno-21-17"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-21-18" id="__codelineno-21-18" name="__codelineno-21-18"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">.</span><span class="n">contains</span><span class="p">(</span><span class="n">choice</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-21-19" id="__codelineno-21-19" name="__codelineno-21-19"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-21-20" id="__codelineno-21-20" name="__codelineno-21-20"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-21-21" id="__codelineno-21-21" name="__codelineno-21-21"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-21-22" id="__codelineno-21-22" name="__codelineno-21-22"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-21-23" id="__codelineno-21-23" name="__codelineno-21-23"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-21-24" id="__codelineno-21-24" name="__codelineno-21-24"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-21-25" id="__codelineno-21-25" name="__codelineno-21-25"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-21-26" id="__codelineno-21-26" name="__codelineno-21-26"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-21-27" id="__codelineno-21-27" name="__codelineno-21-27"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">removeLast</span><span class="p">();</span>
<a href="#__codelineno-21-28" id="__codelineno-21-28" name="__codelineno-21-28"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-21-29" id="__codelineno-21-29" name="__codelineno-21-29"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-21-30" id="__codelineno-21-30" name="__codelineno-21-30"></a><span class="p">}</span>
<a href="#__codelineno-21-31" id="__codelineno-21-31" name="__codelineno-21-31"></a>
<a href="#__codelineno-21-32" id="__codelineno-21-32" name="__codelineno-21-32"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-21-33" id="__codelineno-21-33" name="__codelineno-21-33"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">permutationsII</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">nums</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-21-34" id="__codelineno-21-34" name="__codelineno-21-34"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-21-35" id="__codelineno-21-35" name="__codelineno-21-35"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">([],</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">filled</span><span class="p">(</span><span class="n">nums</span><span class="p">.</span><span class="n">length</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">),</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-21-36" id="__codelineno-21-36" name="__codelineno-21-36"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-21-37" id="__codelineno-21-37" name="__codelineno-21-37"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.rs</span><pre><span></span><code><a href="#__codelineno-22-1" id="__codelineno-22-1" name="__codelineno-22-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-22-2" id="__codelineno-22-2" name="__codelineno-22-2"></a><span class="k">fn</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="k">mut</span><span class="w"> </span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="p">[</span><span class="kt">i32</span><span class="p">],</span><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="p">[</span><span class="kt">bool</span><span class="p">],</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;&gt;</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-22-3" id="__codelineno-22-3" name="__codelineno-22-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-22-4" id="__codelineno-22-4" name="__codelineno-22-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-22-5" id="__codelineno-22-5" name="__codelineno-22-5"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">push</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<a href="#__codelineno-22-6" id="__codelineno-22-6" name="__codelineno-22-6"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-22-7" id="__codelineno-22-7" name="__codelineno-22-7"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-22-8" id="__codelineno-22-8" name="__codelineno-22-8"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-22-9" id="__codelineno-22-9" name="__codelineno-22-9"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">HashSet</span><span class="p">::</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">::</span><span class="n">new</span><span class="p">();</span>
<a href="#__codelineno-22-10" id="__codelineno-22-10" name="__codelineno-22-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="mi">0</span><span class="o">..</span><span class="n">choices</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-22-11" id="__codelineno-22-11" name="__codelineno-22-11"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-22-12" id="__codelineno-22-12" name="__codelineno-22-12"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-22-13" id="__codelineno-22-13" name="__codelineno-22-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">.</span><span class="n">contains</span><span class="p">(</span><span class="o">&amp;</span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-22-14" id="__codelineno-22-14" name="__codelineno-22-14"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-22-15" id="__codelineno-22-15" name="__codelineno-22-15"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="n">insert</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-22-16" id="__codelineno-22-16" name="__codelineno-22-16"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a href="#__codelineno-22-17" id="__codelineno-22-17" name="__codelineno-22-17"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">push</span><span class="p">(</span><span class="n">choice</span><span class="p">);</span>
<a href="#__codelineno-22-18" id="__codelineno-22-18" name="__codelineno-22-18"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-22-19" id="__codelineno-22-19" name="__codelineno-22-19"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">clone</span><span class="p">(),</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-22-20" id="__codelineno-22-20" name="__codelineno-22-20"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-22-21" id="__codelineno-22-21" name="__codelineno-22-21"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span>
<a href="#__codelineno-22-22" id="__codelineno-22-22" name="__codelineno-22-22"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="n">pop</span><span class="p">();</span>
<a href="#__codelineno-22-23" id="__codelineno-22-23" name="__codelineno-22-23"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-22-24" id="__codelineno-22-24" name="__codelineno-22-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-22-25" id="__codelineno-22-25" name="__codelineno-22-25"></a><span class="p">}</span>
<a href="#__codelineno-22-26" id="__codelineno-22-26" name="__codelineno-22-26"></a>
<a href="#__codelineno-22-27" id="__codelineno-22-27" name="__codelineno-22-27"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-22-28" id="__codelineno-22-28" name="__codelineno-22-28"></a><span class="k">fn</span><span class="w"> </span><span class="nf">permutations_ii</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span><span class="w"> </span><span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="p">[</span><span class="kt">i32</span><span class="p">])</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-22-29" id="__codelineno-22-29" name="__codelineno-22-29"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Vec</span><span class="p">::</span><span class="n">new</span><span class="p">();</span>
<a href="#__codelineno-22-30" id="__codelineno-22-30" name="__codelineno-22-30"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="nb">Vec</span><span class="p">::</span><span class="n">new</span><span class="p">(),</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="fm">vec!</span><span class="p">[</span><span class="kc">false</span><span class="p">;</span><span class="w"> </span><span class="n">nums</span><span class="p">.</span><span class="n">len</span><span class="p">()],</span><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">res</span><span class="p">);</span>
<a href="#__codelineno-22-31" id="__codelineno-22-31" name="__codelineno-22-31"></a><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-22-32" id="__codelineno-22-32" name="__codelineno-22-32"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.c</span><pre><span></span><code><a href="#__codelineno-23-1" id="__codelineno-23-1" name="__codelineno-23-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-23-2" id="__codelineno-23-2" name="__codelineno-23-2"></a><span class="kt">void</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">stateSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">,</span><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="o">*</span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">resSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-3" id="__codelineno-23-3" name="__codelineno-23-3"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-23-4" id="__codelineno-23-4" name="__codelineno-23-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">stateSize</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-5" id="__codelineno-23-5" name="__codelineno-23-5"></a><span class="w"> </span><span class="n">res</span><span class="p">[</span><span class="o">*</span><span class="n">resSize</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">choicesSize</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span>
<a href="#__codelineno-23-6" id="__codelineno-23-6" name="__codelineno-23-6"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-7" id="__codelineno-23-7" name="__codelineno-23-7"></a><span class="w"> </span><span class="n">res</span><span class="p">[</span><span class="o">*</span><span class="n">resSize</span><span class="p">][</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-23-8" id="__codelineno-23-8" name="__codelineno-23-8"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-23-9" id="__codelineno-23-9" name="__codelineno-23-9"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">resSize</span><span class="p">)</span><span class="o">++</span><span class="p">;</span>
<a href="#__codelineno-23-10" id="__codelineno-23-10" name="__codelineno-23-10"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-23-11" id="__codelineno-23-11" name="__codelineno-23-11"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-23-12" id="__codelineno-23-12" name="__codelineno-23-12"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-23-13" id="__codelineno-23-13" name="__codelineno-23-13"></a><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">duplicated</span><span class="p">[</span><span class="n">MAX_SIZE</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="nb">false</span><span class="p">};</span>
<a href="#__codelineno-23-14" id="__codelineno-23-14" name="__codelineno-23-14"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-15" id="__codelineno-23-15" name="__codelineno-23-15"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<a href="#__codelineno-23-16" id="__codelineno-23-16" name="__codelineno-23-16"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-23-17" id="__codelineno-23-17" name="__codelineno-23-17"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">[</span><span class="n">choice</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-18" id="__codelineno-23-18" name="__codelineno-23-18"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-23-19" id="__codelineno-23-19" name="__codelineno-23-19"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">[</span><span class="n">choice</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-23-20" id="__codelineno-23-20" name="__codelineno-23-20"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<a href="#__codelineno-23-21" id="__codelineno-23-21" name="__codelineno-23-21"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">stateSize</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choice</span><span class="p">;</span>
<a href="#__codelineno-23-22" id="__codelineno-23-22" name="__codelineno-23-22"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-23-23" id="__codelineno-23-23" name="__codelineno-23-23"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">stateSize</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">choicesSize</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">resSize</span><span class="p">);</span>
<a href="#__codelineno-23-24" id="__codelineno-23-24" name="__codelineno-23-24"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-23-25" id="__codelineno-23-25" name="__codelineno-23-25"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<a href="#__codelineno-23-26" id="__codelineno-23-26" name="__codelineno-23-26"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-23-27" id="__codelineno-23-27" name="__codelineno-23-27"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-23-28" id="__codelineno-23-28" name="__codelineno-23-28"></a><span class="p">}</span>
<a href="#__codelineno-23-29" id="__codelineno-23-29" name="__codelineno-23-29"></a>
<a href="#__codelineno-23-30" id="__codelineno-23-30" name="__codelineno-23-30"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-23-31" id="__codelineno-23-31" name="__codelineno-23-31"></a><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="nf">permutationsII</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">numsSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">returnSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-32" id="__codelineno-23-32" name="__codelineno-23-32"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">numsSize</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span>
<a href="#__codelineno-23-33" id="__codelineno-23-33" name="__codelineno-23-33"></a><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="o">*</span><span class="n">selected</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">bool</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">numsSize</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">bool</span><span class="p">));</span>
<a href="#__codelineno-23-34" id="__codelineno-23-34" name="__codelineno-23-34"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">numsSize</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-23-35" id="__codelineno-23-35" name="__codelineno-23-35"></a><span class="w"> </span><span class="n">selected</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<a href="#__codelineno-23-36" id="__codelineno-23-36" name="__codelineno-23-36"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-23-37" id="__codelineno-23-37" name="__codelineno-23-37"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">**</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="n">MAX_SIZE</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">));</span>
<a href="#__codelineno-23-38" id="__codelineno-23-38" name="__codelineno-23-38"></a><span class="w"> </span><span class="o">*</span><span class="n">returnSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<a href="#__codelineno-23-39" id="__codelineno-23-39" name="__codelineno-23-39"></a>
<a href="#__codelineno-23-40" id="__codelineno-23-40" name="__codelineno-23-40"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">numsSize</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">returnSize</span><span class="p">);</span>
<a href="#__codelineno-23-41" id="__codelineno-23-41" name="__codelineno-23-41"></a>
<a href="#__codelineno-23-42" id="__codelineno-23-42" name="__codelineno-23-42"></a><span class="w"> </span><span class="n">free</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<a href="#__codelineno-23-43" id="__codelineno-23-43" name="__codelineno-23-43"></a><span class="w"> </span><span class="n">free</span><span class="p">(</span><span class="n">selected</span><span class="p">);</span>
<a href="#__codelineno-23-44" id="__codelineno-23-44" name="__codelineno-23-44"></a>
<a href="#__codelineno-23-45" id="__codelineno-23-45" name="__codelineno-23-45"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-23-46" id="__codelineno-23-46" name="__codelineno-23-46"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.kt</span><pre><span></span><code><a href="#__codelineno-24-1" id="__codelineno-24-1" name="__codelineno-24-1"></a><span class="cm">/* 回溯算法:全排列 II */</span>
<a href="#__codelineno-24-2" id="__codelineno-24-2" name="__codelineno-24-2"></a><span class="kd">fun</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span>
<a href="#__codelineno-24-3" id="__codelineno-24-3" name="__codelineno-24-3"></a><span class="w"> </span><span class="n">state</span><span class="p">:</span><span class="w"> </span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;</span><span class="p">,</span>
<a href="#__codelineno-24-4" id="__codelineno-24-4" name="__codelineno-24-4"></a><span class="w"> </span><span class="n">choices</span><span class="p">:</span><span class="w"> </span><span class="n">IntArray</span><span class="p">,</span>
<a href="#__codelineno-24-5" id="__codelineno-24-5" name="__codelineno-24-5"></a><span class="w"> </span><span class="n">selected</span><span class="p">:</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">,</span>
<a href="#__codelineno-24-6" id="__codelineno-24-6" name="__codelineno-24-6"></a><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="n">MutableList</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;?&gt;</span>
<a href="#__codelineno-24-7" id="__codelineno-24-7" name="__codelineno-24-7"></a><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-24-8" id="__codelineno-24-8" name="__codelineno-24-8"></a><span class="w"> </span><span class="c1">// 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-24-9" id="__codelineno-24-9" name="__codelineno-24-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">size</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-24-10" id="__codelineno-24-10" name="__codelineno-24-10"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">toMutableList</span><span class="p">())</span>
<a href="#__codelineno-24-11" id="__codelineno-24-11" name="__codelineno-24-11"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-24-12" id="__codelineno-24-12" name="__codelineno-24-12"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-24-13" id="__codelineno-24-13" name="__codelineno-24-13"></a><span class="w"> </span><span class="c1">// 遍历所有选择</span>
<a href="#__codelineno-24-14" id="__codelineno-24-14" name="__codelineno-24-14"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">HashSet</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;</span><span class="p">()</span>
<a href="#__codelineno-24-15" id="__codelineno-24-15" name="__codelineno-24-15"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">choices</span><span class="p">.</span><span class="na">indices</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-24-16" id="__codelineno-24-16" name="__codelineno-24-16"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">choice</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">choices</span><span class="o">[</span><span class="n">i</span><span class="o">]</span>
<a href="#__codelineno-24-17" id="__codelineno-24-17" name="__codelineno-24-17"></a><span class="w"> </span><span class="c1">// 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-24-18" id="__codelineno-24-18" name="__codelineno-24-18"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="p">.</span><span class="na">contains</span><span class="p">(</span><span class="n">choice</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-24-19" id="__codelineno-24-19" name="__codelineno-24-19"></a><span class="w"> </span><span class="c1">// 尝试:做出选择,更新状态</span>
<a href="#__codelineno-24-20" id="__codelineno-24-20" name="__codelineno-24-20"></a><span class="w"> </span><span class="n">duplicated</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span><span class="w"> </span><span class="c1">// 记录选择过的元素值</span>
<a href="#__codelineno-24-21" id="__codelineno-24-21" name="__codelineno-24-21"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-24-22" id="__codelineno-24-22" name="__codelineno-24-22"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-24-23" id="__codelineno-24-23" name="__codelineno-24-23"></a><span class="w"> </span><span class="c1">// 进行下一轮选择</span>
<a href="#__codelineno-24-24" id="__codelineno-24-24" name="__codelineno-24-24"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-24-25" id="__codelineno-24-25" name="__codelineno-24-25"></a><span class="w"> </span><span class="c1">// 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-24-26" id="__codelineno-24-26" name="__codelineno-24-26"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-24-27" id="__codelineno-24-27" name="__codelineno-24-27"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">removeAt</span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="na">size</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">)</span>
<a href="#__codelineno-24-28" id="__codelineno-24-28" name="__codelineno-24-28"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-24-29" id="__codelineno-24-29" name="__codelineno-24-29"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-24-30" id="__codelineno-24-30" name="__codelineno-24-30"></a><span class="p">}</span>
<a href="#__codelineno-24-31" id="__codelineno-24-31" name="__codelineno-24-31"></a>
<a href="#__codelineno-24-32" id="__codelineno-24-32" name="__codelineno-24-32"></a><span class="cm">/* 全排列 II */</span>
<a href="#__codelineno-24-33" id="__codelineno-24-33" name="__codelineno-24-33"></a><span class="kd">fun</span><span class="w"> </span><span class="nf">permutationsII</span><span class="p">(</span><span class="n">nums</span><span class="p">:</span><span class="w"> </span><span class="n">IntArray</span><span class="p">):</span><span class="w"> </span><span class="n">MutableList</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;?&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-24-34" id="__codelineno-24-34" name="__codelineno-24-34"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">mutableListOf</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">Int</span><span class="o">&gt;?&gt;</span><span class="p">()</span>
<a href="#__codelineno-24-35" id="__codelineno-24-35" name="__codelineno-24-35"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">mutableListOf</span><span class="p">(),</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">(</span><span class="n">nums</span><span class="p">.</span><span class="na">size</span><span class="p">),</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-24-36" id="__codelineno-24-36" name="__codelineno-24-36"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-24-37" id="__codelineno-24-37" name="__codelineno-24-37"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">permutations_ii.rb</span><pre><span></span><code><a href="#__codelineno-25-1" id="__codelineno-25-1" name="__codelineno-25-1"></a><span class="c1">### 回溯算法:全排列 II ###</span>
<a href="#__codelineno-25-2" id="__codelineno-25-2" name="__codelineno-25-2"></a><span class="k">def</span><span class="w"> </span><span class="nf">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-25-3" id="__codelineno-25-3" name="__codelineno-25-3"></a><span class="w"> </span><span class="c1"># 当状态长度等于元素数量时,记录解</span>
<a href="#__codelineno-25-4" id="__codelineno-25-4" name="__codelineno-25-4"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">state</span><span class="o">.</span><span class="n">length</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">choices</span><span class="o">.</span><span class="n">length</span>
<a href="#__codelineno-25-5" id="__codelineno-25-5" name="__codelineno-25-5"></a><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">state</span><span class="o">.</span><span class="n">dup</span>
<a href="#__codelineno-25-6" id="__codelineno-25-6" name="__codelineno-25-6"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-25-7" id="__codelineno-25-7" name="__codelineno-25-7"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-25-8" id="__codelineno-25-8" name="__codelineno-25-8"></a>
<a href="#__codelineno-25-9" id="__codelineno-25-9" name="__codelineno-25-9"></a><span class="w"> </span><span class="c1"># 遍历所有选择</span>
<a href="#__codelineno-25-10" id="__codelineno-25-10" name="__codelineno-25-10"></a><span class="w"> </span><span class="n">duplicated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">Set</span><span class="o">.</span><span class="n">new</span>
<a href="#__codelineno-25-11" id="__codelineno-25-11" name="__codelineno-25-11"></a><span class="w"> </span><span class="n">choices</span><span class="o">.</span><span class="n">each_with_index</span><span class="w"> </span><span class="k">do</span><span class="w"> </span><span class="o">|</span><span class="n">choice</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="o">|</span>
<a href="#__codelineno-25-12" id="__codelineno-25-12" name="__codelineno-25-12"></a><span class="w"> </span><span class="c1"># 剪枝:不允许重复选择元素 且 不允许重复选择相等元素</span>
<a href="#__codelineno-25-13" id="__codelineno-25-13" name="__codelineno-25-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="o">!</span><span class="n">duplicated</span><span class="o">.</span><span class="n">include?</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-25-14" id="__codelineno-25-14" name="__codelineno-25-14"></a><span class="w"> </span><span class="c1"># 尝试:做出选择,更新状态</span>
<a href="#__codelineno-25-15" id="__codelineno-25-15" name="__codelineno-25-15"></a><span class="w"> </span><span class="n">duplicated</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
<a href="#__codelineno-25-16" id="__codelineno-25-16" name="__codelineno-25-16"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kp">true</span>
<a href="#__codelineno-25-17" id="__codelineno-25-17" name="__codelineno-25-17"></a><span class="w"> </span><span class="n">state</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">choice</span>
<a href="#__codelineno-25-18" id="__codelineno-25-18" name="__codelineno-25-18"></a><span class="w"> </span><span class="c1"># 进行下一轮选择</span>
<a href="#__codelineno-25-19" id="__codelineno-25-19" name="__codelineno-25-19"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">,</span><span class="w"> </span><span class="n">choices</span><span class="p">,</span><span class="w"> </span><span class="n">selected</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-25-20" id="__codelineno-25-20" name="__codelineno-25-20"></a><span class="w"> </span><span class="c1"># 回退:撤销选择,恢复到之前的状态</span>
<a href="#__codelineno-25-21" id="__codelineno-25-21" name="__codelineno-25-21"></a><span class="w"> </span><span class="n">selected</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kp">false</span>
<a href="#__codelineno-25-22" id="__codelineno-25-22" name="__codelineno-25-22"></a><span class="w"> </span><span class="n">state</span><span class="o">.</span><span class="n">pop</span>
<a href="#__codelineno-25-23" id="__codelineno-25-23" name="__codelineno-25-23"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-25-24" id="__codelineno-25-24" name="__codelineno-25-24"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-25-25" id="__codelineno-25-25" name="__codelineno-25-25"></a><span class="k">end</span>
<a href="#__codelineno-25-26" id="__codelineno-25-26" name="__codelineno-25-26"></a>
<a href="#__codelineno-25-27" id="__codelineno-25-27" name="__codelineno-25-27"></a><span class="c1">### 全排列 II ###</span>
<a href="#__codelineno-25-28" id="__codelineno-25-28" name="__codelineno-25-28"></a><span class="k">def</span><span class="w"> </span><span class="nf">permutations_ii</span><span class="p">(</span><span class="n">nums</span><span class="p">)</span>
<a href="#__codelineno-25-29" id="__codelineno-25-29" name="__codelineno-25-29"></a><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">[]</span>
<a href="#__codelineno-25-30" id="__codelineno-25-30" name="__codelineno-25-30"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="o">[]</span><span class="p">,</span><span class="w"> </span><span class="n">nums</span><span class="p">,</span><span class="w"> </span><span class="nb">Array</span><span class="o">.</span><span class="n">new</span><span class="p">(</span><span class="n">nums</span><span class="o">.</span><span class="n">length</span><span class="p">,</span><span class="w"> </span><span class="kp">false</span><span class="p">),</span><span class="w"> </span><span class="n">res</span><span class="p">)</span>
<a href="#__codelineno-25-31" id="__codelineno-25-31" name="__codelineno-25-31"></a><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-25-32" id="__codelineno-25-32" name="__codelineno-25-32"></a><span class="k">end</span>
</code></pre></div>
</div>
</div>
</div>
<details class="pythontutor">
<summary>可视化运行</summary>
<p><div style="height: 549px; width: 100%;"><iframe class="pythontutor-iframe" src="https://pythontutor.com/iframe-embed.html#code=def%20backtrack%28%0A%20%20%20%20state%3A%20list%5Bint%5D,%20choices%3A%20list%5Bint%5D,%20selected%3A%20list%5Bbool%5D,%20res%3A%20list%5Blist%5Bint%5D%5D%0A%29%3A%0A%20%20%20%20%22%22%22%E5%9B%9E%E6%BA%AF%E7%AE%97%E6%B3%95%EF%BC%9A%E5%85%A8%E6%8E%92%E5%88%97%20II%22%22%22%0A%20%20%20%20%23%20%E5%BD%93%E7%8A%B6%E6%80%81%E9%95%BF%E5%BA%A6%E7%AD%89%E4%BA%8E%E5%85%83%E7%B4%A0%E6%95%B0%E9%87%8F%E6%97%B6%EF%BC%8C%E8%AE%B0%E5%BD%95%E8%A7%A3%0A%20%20%20%20if%20len%28state%29%20%3D%3D%20len%28choices%29%3A%0A%20%20%20%20%20%20%20%20res.append%28list%28state%29%29%0A%20%20%20%20%20%20%20%20return%0A%20%20%20%20%23%20%E9%81%8D%E5%8E%86%E6%89%80%E6%9C%89%E9%80%89%E6%8B%A9%0A%20%20%20%20duplicated%20%3D%20set%5Bint%5D%28%29%0A%20%20%20%20for%20i,%20choice%20in%20enumerate%28choices%29%3A%0A%20%20%20%20%20%20%20%20%23%20%E5%89%AA%E6%9E%9D%EF%BC%9A%E4%B8%8D%E5%85%81%E8%AE%B8%E9%87%8D%E5%A4%8D%E9%80%89%E6%8B%A9%E5%85%83%E7%B4%A0%20%E4%B8%94%20%E4%B8%8D%E5%85%81%E8%AE%B8%E9%87%8D%E5%A4%8D%E9%80%89%E6%8B%A9%E7%9B%B8%E7%AD%89%E5%85%83%E7%B4%A0%0A%20%20%20%20%20%20%20%20if%20not%20selected%5Bi%5D%20and%20choice%20not%20in%20duplicated%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%B0%9D%E8%AF%95%EF%BC%9A%E5%81%9A%E5%87%BA%E9%80%89%E6%8B%A9%EF%BC%8C%E6%9B%B4%E6%96%B0%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20duplicated.add%28choice%29%20%20%23%20%E8%AE%B0%E5%BD%95%E9%80%89%E6%8B%A9%E8%BF%87%E7%9A%84%E5%85%83%E7%B4%A0%E5%80%BC%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20True%0A%20%20%20%20%20%20%20%20%20%20%20%20state.append%28choice%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E8%BF%9B%E8%A1%8C%E4%B8%8B%E4%B8%80%E8%BD%AE%E9%80%89%E6%8B%A9%0A%20%20%20%20%20%20%20%20%20%20%20%20backtrack%28state,%20choices,%20selected,%20res%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%9B%9E%E9%80%80%EF%BC%9A%E6%92%A4%E9%94%80%E9%80%89%E6%8B%A9%EF%BC%8C%E6%81%A2%E5%A4%8D%E5%88%B0%E4%B9%8B%E5%89%8D%E7%9A%84%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20False%0A%20%20%20%20%20%20%20%20%20%20%20%20state.pop%28%29%0A%0A%0Adef%20permutations_ii%28nums%3A%20list%5Bint%5D%29%20-%3E%20list%5Blist%5Bint%5D%5D%3A%0A%20%20%20%20%22%22%22%E5%85%A8%E6%8E%92%E5%88%97%20II%22%22%22%0A%20%20%20%20res%20%3D%20%5B%5D%0A%20%20%20%20backtrack%28state%3D%5B%5D,%20choices%3Dnums,%20selected%3D%5BFalse%5D%20*%20len%28nums%29,%20res%3Dres%29%0A%20%20%20%20return%20res%0A%0A%0A%22%22%22Driver%20Code%22%22%22%0Aif%20__name__%20%3D%3D%20%22__main__%22%3A%0A%20%20%20%20nums%20%3D%20%5B1,%202,%202%5D%0A%0A%20%20%20%20res%20%3D%20permutations_ii%28nums%29%0A%0A%20%20%20%20print%28f%22%E8%BE%93%E5%85%A5%E6%95%B0%E7%BB%84%20nums%20%3D%20%7Bnums%7D%22%29%0A%20%20%20%20print%28f%22%E6%89%80%E6%9C%89%E6%8E%92%E5%88%97%20res%20%3D%20%7Bres%7D%22%29&amp;codeDivHeight=472&amp;codeDivWidth=350&amp;cumulative=false&amp;curInstr=13&amp;heapPrimitives=nevernest&amp;origin=opt-frontend.js&amp;py=311&amp;rawInputLstJSON=%5B%5D&amp;textReferences=false" title="可视化运行"> </iframe></div>
<div style="margin-top: 5px;"><a href="https://pythontutor.com/iframe-embed.html#code=def%20backtrack%28%0A%20%20%20%20state%3A%20list%5Bint%5D,%20choices%3A%20list%5Bint%5D,%20selected%3A%20list%5Bbool%5D,%20res%3A%20list%5Blist%5Bint%5D%5D%0A%29%3A%0A%20%20%20%20%22%22%22%E5%9B%9E%E6%BA%AF%E7%AE%97%E6%B3%95%EF%BC%9A%E5%85%A8%E6%8E%92%E5%88%97%20II%22%22%22%0A%20%20%20%20%23%20%E5%BD%93%E7%8A%B6%E6%80%81%E9%95%BF%E5%BA%A6%E7%AD%89%E4%BA%8E%E5%85%83%E7%B4%A0%E6%95%B0%E9%87%8F%E6%97%B6%EF%BC%8C%E8%AE%B0%E5%BD%95%E8%A7%A3%0A%20%20%20%20if%20len%28state%29%20%3D%3D%20len%28choices%29%3A%0A%20%20%20%20%20%20%20%20res.append%28list%28state%29%29%0A%20%20%20%20%20%20%20%20return%0A%20%20%20%20%23%20%E9%81%8D%E5%8E%86%E6%89%80%E6%9C%89%E9%80%89%E6%8B%A9%0A%20%20%20%20duplicated%20%3D%20set%5Bint%5D%28%29%0A%20%20%20%20for%20i,%20choice%20in%20enumerate%28choices%29%3A%0A%20%20%20%20%20%20%20%20%23%20%E5%89%AA%E6%9E%9D%EF%BC%9A%E4%B8%8D%E5%85%81%E8%AE%B8%E9%87%8D%E5%A4%8D%E9%80%89%E6%8B%A9%E5%85%83%E7%B4%A0%20%E4%B8%94%20%E4%B8%8D%E5%85%81%E8%AE%B8%E9%87%8D%E5%A4%8D%E9%80%89%E6%8B%A9%E7%9B%B8%E7%AD%89%E5%85%83%E7%B4%A0%0A%20%20%20%20%20%20%20%20if%20not%20selected%5Bi%5D%20and%20choice%20not%20in%20duplicated%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%B0%9D%E8%AF%95%EF%BC%9A%E5%81%9A%E5%87%BA%E9%80%89%E6%8B%A9%EF%BC%8C%E6%9B%B4%E6%96%B0%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20duplicated.add%28choice%29%20%20%23%20%E8%AE%B0%E5%BD%95%E9%80%89%E6%8B%A9%E8%BF%87%E7%9A%84%E5%85%83%E7%B4%A0%E5%80%BC%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20True%0A%20%20%20%20%20%20%20%20%20%20%20%20state.append%28choice%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E8%BF%9B%E8%A1%8C%E4%B8%8B%E4%B8%80%E8%BD%AE%E9%80%89%E6%8B%A9%0A%20%20%20%20%20%20%20%20%20%20%20%20backtrack%28state,%20choices,%20selected,%20res%29%0A%20%20%20%20%20%20%20%20%20%20%20%20%23%20%E5%9B%9E%E9%80%80%EF%BC%9A%E6%92%A4%E9%94%80%E9%80%89%E6%8B%A9%EF%BC%8C%E6%81%A2%E5%A4%8D%E5%88%B0%E4%B9%8B%E5%89%8D%E7%9A%84%E7%8A%B6%E6%80%81%0A%20%20%20%20%20%20%20%20%20%20%20%20selected%5Bi%5D%20%3D%20False%0A%20%20%20%20%20%20%20%20%20%20%20%20state.pop%28%29%0A%0A%0Adef%20permutations_ii%28nums%3A%20list%5Bint%5D%29%20-%3E%20list%5Blist%5Bint%5D%5D%3A%0A%20%20%20%20%22%22%22%E5%85%A8%E6%8E%92%E5%88%97%20II%22%22%22%0A%20%20%20%20res%20%3D%20%5B%5D%0A%20%20%20%20backtrack%28state%3D%5B%5D,%20choices%3Dnums,%20selected%3D%5BFalse%5D%20*%20len%28nums%29,%20res%3Dres%29%0A%20%20%20%20return%20res%0A%0A%0A%22%22%22Driver%20Code%22%22%22%0Aif%20__name__%20%3D%3D%20%22__main__%22%3A%0A%20%20%20%20nums%20%3D%20%5B1,%202,%202%5D%0A%0A%20%20%20%20res%20%3D%20permutations_ii%28nums%29%0A%0A%20%20%20%20print%28f%22%E8%BE%93%E5%85%A5%E6%95%B0%E7%BB%84%20nums%20%3D%20%7Bnums%7D%22%29%0A%20%20%20%20print%28f%22%E6%89%80%E6%9C%89%E6%8E%92%E5%88%97%20res%20%3D%20%7Bres%7D%22%29&amp;codeDivHeight=800&amp;codeDivWidth=600&amp;cumulative=false&amp;curInstr=13&amp;heapPrimitives=nevernest&amp;origin=opt-frontend.js&amp;py=311&amp;rawInputLstJSON=%5B%5D&amp;textReferences=false" rel="noopener noreferrer" target="_blank">全屏观看 &gt;</a></div></p>
</details>
<p>假设元素两两之间互不相同,则 <span class="arithmatex">\(n\)</span> 个元素共有 <span class="arithmatex">\(n!\)</span> 种排列(阶乘);在记录结果时,需要复制长度为 <span class="arithmatex">\(n\)</span> 的列表,使用 <span class="arithmatex">\(O(n)\)</span> 时间。<strong>因此时间复杂度为 <span class="arithmatex">\(O(n!n)\)</span></strong> 。</p>
<p>最大递归深度为 <span class="arithmatex">\(n\)</span> ,使用 <span class="arithmatex">\(O(n)\)</span> 栈帧空间。<code>selected</code> 使用 <span class="arithmatex">\(O(n)\)</span> 空间。同一时刻最多共有 <span class="arithmatex">\(n\)</span> 个 <code>duplicated</code> ,使用 <span class="arithmatex">\(O(n^2)\)</span> 空间。<strong>因此空间复杂度为 <span class="arithmatex">\(O(n^2)\)</span></strong> 。</p>
<h3 id="3">3.   两种剪枝对比<a class="headerlink" href="#3" title="Permanent link"></a></h3>
<p>请注意,虽然 <code>selected</code> 和 <code>duplicated</code> 都用于剪枝,但两者的目标不同。</p>
<ul>
<li><strong>重复选择剪枝</strong>:整个搜索过程中只有一个 <code>selected</code> 。它记录的是当前状态中包含哪些元素,其作用是避免某个元素在 <code>state</code> 中重复出现。</li>
<li><strong>相等元素剪枝</strong>:每轮选择(每个调用的 <code>backtrack</code> 函数)都包含一个 <code>duplicated</code> 。它记录的是在本轮遍历(<code>for</code> 循环)中哪些元素已被选择过,其作用是保证相等元素只被选择一次。</li>
</ul>
<p>图 13-9 展示了两个剪枝条件的生效范围。注意,树中的每个节点代表一个选择,从根节点到叶节点的路径上的各个节点构成一个排列。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="chapter_backtracking/permutations_problem.assets/permutations_ii_pruning_summary.png" data-dark-src="/assets/figure-svg/figures/6f94280d93f1b14be0d27abd.json" data-src="/assets/figure-svg/figures/d86766a7f78b256a452b0d9e.json" style=";--figure-ratio:960.0/540.0"><object data="/chapter_backtracking/permutations_problem.assets/permutations_ii_pruning_summary.svg" data-theme="light" tabindex="-1" type="image/svg+xml">两种剪枝条件的作用范围</object><object data="/chapter_backtracking/permutations_problem.assets/permutations_ii_pruning_summary.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">两种剪枝条件的作用范围</object></ha-svg-figure></p>
<p align="center"> 图 13-9   两种剪枝条件的作用范围 </p>
<!-- Source file information -->
<!-- Was this page helpful? -->
<!-- Previous and next pages link -->
<nav aria-label="页脚" class="md-footer__inner md-grid">
<!-- Link to previous page -->
<a aria-label="上一页: 13.1 &amp;nbsp; 回溯算法" class="md-footer__link md-footer__link--prev" href="../backtracking_algorithm/" rel="prev">
<div class="md-footer__button md-icon">
<svg class="lucide lucide-arrow-left" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="m12 19-7-7 7-7M19 12H5"></path></svg>
</div>
<div class="md-footer__title">
<span class="md-footer__direction">
上一页
</span>
<div class="md-ellipsis">
13.1   回溯算法
</div>
</div>
</a>
<!-- Link to next page -->
<a aria-label="下一页: 13.3 &amp;nbsp; 子集和问题" class="md-footer__link md-footer__link--next" href="../subset_sum_problem/" rel="next">
<div class="md-footer__title">
<span class="md-footer__direction">
下一页
</span>
<div class="md-ellipsis">
13.3   子集和问题
</div>
</div>
<div class="md-footer__button md-icon">
<svg class="lucide lucide-arrow-right" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M5 12h14M12 5l7 7-7 7"></path></svg>
</div>
</a>
</nav>
<!-- Comment system -->
<!-- Check-in button above comments -->
<h5 align="center" id="__comments">欢迎在评论区留下你的见解、问题或建议</h5>
<!-- Insert generated snippet here -->
<script async="" crossorigin="anonymous" data-category="Announcements" data-category-id="DIC_kwDOIXtSq84CSZk_" data-emit-metadata="1" data-input-position="top" data-lang="zh-CN" data-mapping="pathname" data-reactions-enabled="1" data-repo="krahets/hello-algo" data-repo-id="R_kgDOIXtSqw" data-strict="1" data-theme="light" src="https://giscus.app/client.js">
</script>
<!-- Synchronize Giscus theme with palette -->
<script>
var giscus = document.querySelector("script[src*=giscus]")
function getGiscusTheme() {
var palette = __md_get("__palette")
var isDark = palette && typeof palette.color === "object" && palette.color.scheme === "slate"
return isDark ? "noborder_dark" : "light"
}
/* Set palette on initial load */
giscus.setAttribute("data-theme", getGiscusTheme())
/* The Giscus client creates the iframe asynchronously with an English title. */
;(function() {
function labelCommentsFrame() {
var frame = document.querySelector("iframe.giscus-frame")
if (!frame) return false
frame.setAttribute("title", "评论")
return true
}
if (labelCommentsFrame()) return
var observer = new MutationObserver(function() {
if (labelCommentsFrame()) observer.disconnect()
})
observer.observe(giscus.parentElement, { childList: true, subtree: true })
})()
/* Register event handlers after documented loaded */
document.addEventListener("DOMContentLoaded", function() {
var ref = document.querySelector("[data-md-component=palette]")
if (!ref) return
ref.addEventListener("change", function() {
var theme = getGiscusTheme()
/* Instruct Giscus to change theme */
var frame = document.querySelector(".giscus-frame")
if (!frame) return
frame.contentWindow.postMessage(
{ giscus: { setConfig: { theme } } },
"https://giscus.app"
)
})
})
</script>
</article>
</div>
<script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script>
<script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script>
</div>
</main>
<footer class="md-footer">
<div class="md-footer-meta md-typeset">
<div class="md-footer-meta__inner md-grid">
<div class="md-copyright">
<div class="md-copyright__highlight">
Copyright © 2026 krahets<br/>The website content is licensed under <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA 4.0</a>
</div>
</div>
<div class="md-social">
<a class="md-social__link" href="https://github.com/krahets" rel="noopener" target="_blank" title="github.com">
<svg viewbox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><!--! Font Awesome Free 7.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2" fill="currentColor"></path></svg>
</a>
<a class="md-social__link" href="https://twitter.com/krahets" rel="noopener" target="_blank" title="twitter.com">
<svg viewbox="0 0 448 512" xmlns="http://www.w3.org/2000/svg"><!--! Font Awesome Free 7.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc.--><path d="M357.2 48h70.6L273.6 224.2 455 464H313L201.7 318.6 74.5 464H3.8l164.9-188.5L-5.2 48h145.6l100.5 132.9zm-24.8 373.8h39.1L119.1 88h-42z" fill="currentColor"></path></svg>
</a>
<a class="md-social__link" href="https://leetcode.cn/u/jyd/" rel="noopener" target="_blank" title="leetcode.cn">
<svg viewbox="0 0 576 512" xmlns="http://www.w3.org/2000/svg"><!--! Font Awesome Free 7.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc.--><path d="M360.8 1.2c-17-4.9-34.7 5-39.6 22l-128 448c-4.9 17 5 34.7 22 39.6s34.7-5 39.6-22l128-448c4.9-17-5-34.7-22-39.6m64.6 136.1c-12.5 12.5-12.5 32.8 0 45.3l73.4 73.4-73.4 73.4c-12.5 12.5-12.5 32.8 0 45.3s32.8 12.5 45.3 0l96-96c12.5-12.5 12.5-32.8 0-45.3l-96-96c-12.5-12.5-32.8-12.5-45.3 0zm-274.7 0c-12.5-12.5-32.8-12.5-45.3 0l-96 96c-12.5 12.5-12.5 32.8 0 45.3l96 96c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L77.3 256l73.3-73.4c12.5-12.5 12.5-32.8 0-45.3z" fill="currentColor"></path></svg>
</a>
</div>
</div>
</div>
</footer>
</div>
<div class="md-dialog" data-md-component="dialog">
<div class="md-dialog__inner md-typeset"></div>
</div>
<script id="__config" type="application/json">{"annotate":null,"base":"../../","features":["content.action.edit","content.code.annotate","content.code.copy","content.tabs.link","content.tooltips","navigation.indexes","navigation.tracking","search.highlight","search.share","search.suggest","toc.follow"],"search":"../../assets/javascripts/workers/search.b6b7e04f.min.js","tags":null,"translations":{"clipboard.copied":"已复制","clipboard.copy":"复制","search.result.more.one":"在该页上还有 1 个符合条件的结果","search.result.more.other":"在该页上还有 # 个符合条件的结果","search.result.none":"没有找到符合条件的结果","search.result.one":"找到 1 个符合条件的结果","search.result.other":"# 个符合条件的结果","search.result.placeholder":"键入以开始搜索","search.result.term.missing":"缺少","select.version":"选择当前版本"},"version":null}</script>
<script src="../../assets/javascripts/bundle.4019d56ee3c5b0a3dedbc391860c6a94219c682a362eed02d260bc13cf55232c.min.js"></script>
<script src="../../javascripts/mathjax.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/3.2.2/es5/tex-mml-chtml.min.js"></script>
<script src="../../javascripts/animation_player.js"></script>
<script defer="" src="/assets/figure-svg/js/bcdea376f01bc2bc0cac7c6c.js"></script><script defer="" src="/assets/figure-svg/js/e84f59519170c0f5ef238548.js"></script><script defer="" src="/assets/figure-svg/js/99a707e9f0a14d8280f16808.js"></script><script defer="" src="/assets/figure-svg/js/b789dc8b01e43e756fc89964.js"></script></body>
</html>