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第 1 章   アルゴリズムとの出会い
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第 1 章   アルゴリズムとの出会い
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1.1   アルゴリズムはどこにでもある
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1.2   アルゴリズムとは
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1.3   まとめ
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第 2 章   計算量の解析
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第 2 章   計算量の解析
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2.1   アルゴリズムの効率の評価
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2.2   反復と再帰
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2.3   時間計算量
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2.4   空間計算量
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2.5   まとめ
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2.6   練習問題
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第 3 章   データ構造
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第 3 章   データ構造
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3.1   データ構造の分類
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3.2   基本データ型
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3.3   数値の符号化 *
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3.4   文字エンコーディング *
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3.5   まとめ
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3.6   練習問題
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第 4 章   配列と連結リスト
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第 4 章   配列と連結リスト
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4.1   配列
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4.2   連結リスト
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4.3   リスト
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4.4   メモリとキャッシュ *
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4.5   まとめ
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4.6   練習問題
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第 5 章   スタックとキュー
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第 5 章   スタックとキュー
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5.1   スタック
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5.2   キュー
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5.3   両端キュー
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5.4   まとめ
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5.5   練習問題
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第 6 章   ハッシュテーブル
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第 6 章   ハッシュテーブル
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6.1   ハッシュテーブル
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6.2   ハッシュ衝突
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6.3   ハッシュアルゴリズム
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6.4   まとめ
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6.5   練習問題
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第 7 章   木
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第 7 章   木
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7.1   二分木
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7.2   二分木の走査
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7.3   二分木の配列表現
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7.4   二分探索木
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7.5   AVL 木 *
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7.6   まとめ
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7.7   練習問題
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第 8 章   ヒープ
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第 8 章   ヒープ
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8.1   ヒープ
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8.2   ヒープの構築
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8.3   Top-k 問題
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8.4   まとめ
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8.5   練習問題
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第 9 章   グラフ
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第 9 章   グラフ
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9.1   グラフ
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9.2   グラフの基本操作
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9.3   グラフの走査
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9.4   まとめ
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9.5   練習問題
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第 10 章   探索
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第 10 章   探索
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10.1   二分探索
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10.2   二分探索で挿入位置を探す
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10.3   二分探索で境界を探す
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10.4   ハッシュを使った最適化
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10.5   探索アルゴリズムを改めて考える
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10.6   まとめ
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10.7   練習問題
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第 11 章   ソート
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第 11 章   ソート
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11.1   ソートアルゴリズム
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11.2   選択ソート
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11.3   バブルソート
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11.4   挿入ソート
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11.5   クイックソート
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11.6   マージソート
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11.7   ヒープソート
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11.8   バケットソート
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11.9   カウントソート
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11.10   基数ソート
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11.11   まとめ
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11.12   練習問題
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第 12 章   分割統治
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第 12 章   分割統治
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12.1   分割統治アルゴリズム
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12.2   分割統治による探索戦略
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12.3   二分木の構築問題
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12.4   ハノイの塔の問題
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12.5   まとめ
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12.6   練習問題
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第 13 章   バックトラッキング
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第 13 章   バックトラッキング
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13.1   バックトラッキングアルゴリズム
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13.2   順列列挙問題
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13.3   部分集合和問題
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13.4   n クイーン問題
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13.4   n クイーン問題
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1.   行ごとに配置する戦略
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2.   列と対角線による枝刈り
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3.   コードの実装
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13.5   まとめ
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13.6   練習問題
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第 14 章   動的計画法
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第 14 章   動的計画法
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14.1   動的計画法への第一歩
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14.2   動的計画法の問題の特徴
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14.3   動的計画法の解き方
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14.4   0-1 ナップサック問題
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14.5   個数制限なしナップサック問題
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14.6   編集距離問題
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14.7   まとめ
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14.8   練習問題
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第 15 章   貪欲法
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1.   行ごとに配置する戦略
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2.   列と対角線による枝刈り
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<a class="md-content__button md-icon" href="https://github.com/krahets/hello-algo/tree/main/ja/docs/chapter_backtracking/n_queens_problem.md" title="編集">
<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>
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<h1 id="134-n">13.4   n クイーン問題<a class="headerlink" href="#134-n" title="この見出しへのリンク"></a></h1>
<div class="admonition question">
<p class="admonition-title">問題</p>
<p>チェスの規則では、クイーンは同じ行、列、斜めの線上にある駒を攻撃できます。<span class="arithmatex">\(n\)</span> 個のクイーンと <span class="arithmatex">\(n \times n\)</span> の盤面が与えられたとき、どのクイーン同士も攻撃できない配置を求めてください。</p>
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<p>図 13-15 のように、<span class="arithmatex">\(n = 4\)</span> の場合は二つの解があります。バックトラッキングの観点では、<span class="arithmatex">\(n \times n\)</span> の盤面の <span class="arithmatex">\(n^2\)</span> 個のマスが、すべての選択肢 <code>choices</code> です。クイーンを一つずつ置くたびに盤面が変わり、その時々の盤面が状態 <code>state</code> になります。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="ja/chapter_backtracking/n_queens_problem.assets/solution_4_queens.png" data-dark-src="/assets/figure-svg/figures/a04f59a4b7160034feafe005.json" data-src="/assets/figure-svg/figures/86fa44d26b065b6d593e4348.json" style=";--figure-ratio:960.0/540.0"><object data="/ja/chapter_backtracking/n_queens_problem.assets/solution_4_queens.svg" data-theme="light" tabindex="-1" type="image/svg+xml">4 クイーン問題の解</object><object data="/ja/chapter_backtracking/n_queens_problem.assets/solution_4_queens.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">4 クイーン問題の解</object></ha-svg-figure></p>
<p align="center"> 図 13-15   4 クイーン問題の解 </p>
<p>図 13-16 に、三つの制約条件を示します。<strong>同じ行、同じ列、同じ対角線上に複数のクイーンを置いてはいけません</strong>。対角線には、主対角線方向 <code>\</code> と副対角線方向 <code>/</code> の 2 種類があることに注意してください。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="ja/chapter_backtracking/n_queens_problem.assets/n_queens_constraints.png" data-dark-src="/assets/figure-svg/figures/cfd65359ef8e34f91da2a887.json" data-src="/assets/figure-svg/figures/38e864f3d97738ac6373463b.json" style=";--figure-ratio:960.0/540.0"><object data="/ja/chapter_backtracking/n_queens_problem.assets/n_queens_constraints.svg" data-theme="light" tabindex="-1" type="image/svg+xml">n クイーン問題の制約条件</object><object data="/ja/chapter_backtracking/n_queens_problem.assets/n_queens_constraints.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">n クイーン問題の制約条件</object></ha-svg-figure></p>
<p align="center"> 図 13-16   n クイーン問題の制約条件 </p>
<h3 id="1">1.   行ごとに配置する戦略<a class="headerlink" href="#1" title="この見出しへのリンク"></a></h3>
<p>クイーンの個数と盤面の行数はどちらも <span class="arithmatex">\(n\)</span> なので、<strong>各行にはクイーンをちょうど一つずつ置かなければならない</strong>ことがわかります。</p>
<p>そこで、先頭行から最後の行まで、各行に一つずつ配置する戦略を取れます。</p>
<p>図 13-17 に、4 クイーン問題で行ごとに配置する過程を示します。図の大きさの都合で、先頭行の探索分岐は一つだけを展開し、列と対角線の制約を満たさない配置は枝刈りしています。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="ja/chapter_backtracking/n_queens_problem.assets/n_queens_placing.png" data-dark-src="/assets/figure-svg/figures/b53905cf374abf5b3edcbfca.json" data-src="/assets/figure-svg/figures/74198dae105cd5c939efe6bf.json" style=";--figure-ratio:960.0/540.0"><object data="/ja/chapter_backtracking/n_queens_problem.assets/n_queens_placing.svg" data-theme="light" tabindex="-1" type="image/svg+xml">行ごとに配置する戦略</object><object data="/ja/chapter_backtracking/n_queens_problem.assets/n_queens_placing.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">行ごとに配置する戦略</object></ha-svg-figure></p>
<p align="center"> 図 13-17   行ごとに配置する戦略 </p>
<p>本質的には、<strong>行ごとの配置も枝刈りとして働き</strong>、同じ行に複数のクイーンを置くすべての探索分岐を避けています。</p>
<h3 id="2">2.   列と対角線による枝刈り<a class="headerlink" href="#2" title="この見出しへのリンク"></a></h3>
<p>列の制約を満たすため、長さ <span class="arithmatex">\(n\)</span> のブール配列 <code>cols</code> で、各列にクイーンがあるかを記録します。配置する前に <code>cols</code> を調べ、すでにクイーンがある列を枝刈りします。バックトラッキング中は、<code>cols</code> の状態を動的に更新します。</p>
<div class="admonition tip">
<p class="admonition-title">ヒント</p>
<p>行列の原点は左上にあり、行インデックスは上から下へ、列インデックスは左から右へ増えることに注意してください。</p>
</div>
<p>では、対角線の制約はどう扱えばよいでしょうか。あるマスの行・列インデックスを <span class="arithmatex">\((row, col)\)</span> とします。主対角線方向の線を一つ選ぶと、その線上のすべてのマスでは行インデックスから列インデックスを引いた値が等しく、<strong><span class="arithmatex">\(row - col\)</span> が一定です</strong>。</p>
<p>つまり、二つのマスが <span class="arithmatex">\(row_1 - col_1 = row_2 - col_2\)</span> を満たせば、同じ主対角線方向の線上にあります。この性質を使い、図 13-18 の配列 <code>diags1</code> に、各線上にクイーンがあるかを記録できます。</p>
<p>同様に、<strong>副対角線方向の線上では、すべてのマスの <span class="arithmatex">\(row + col\)</span> が一定です</strong>。配列 <code>diags2</code> を使って、この方向の制約も扱えます。</p>
<p><ha-svg-figure class="animation-figure" data-book-key="ja/chapter_backtracking/n_queens_problem.assets/n_queens_cols_diagonals.png" data-dark-src="/assets/figure-svg/figures/eb039394620025c1ba61510b.json" data-src="/assets/figure-svg/figures/a1c2e3f41c0d6e3d1fd44509.json" style=";--figure-ratio:960.0/540.0"><object data="/ja/chapter_backtracking/n_queens_problem.assets/n_queens_cols_diagonals.svg" data-theme="light" tabindex="-1" type="image/svg+xml">列と対角線の制約の処理</object><object data="/ja/chapter_backtracking/n_queens_problem.assets/n_queens_cols_diagonals.dark.svg" data-theme="dark" tabindex="-1" type="image/svg+xml">列と対角線の制約の処理</object></ha-svg-figure></p>
<p align="center"> 図 13-18   列と対角線の制約の処理 </p>
<h3 id="3">3.   コードの実装<a class="headerlink" href="#3" title="この見出しへのリンク"></a></h3>
<p><span class="arithmatex">\(n\)</span> 次の正方行列では、<span class="arithmatex">\(row - col\)</span> の範囲は <span class="arithmatex">\([-n + 1, n - 1]\)</span>、<span class="arithmatex">\(row + col\)</span> の範囲は <span class="arithmatex">\([0, 2n - 2]\)</span> です。したがって、どちらの方向の対角線も <span class="arithmatex">\(2n - 1\)</span> 本あり、配列 <code>diags1</code> と <code>diags2</code> の長さはいずれも <span class="arithmatex">\(2n - 1\)</span> です。</p>
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<div class="highlight"><span class="filename">n_queens.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">row</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="n">n</span><span class="p">:</span> <span class="nb">int</span><span class="p">,</span>
<a href="#__codelineno-0-4" id="__codelineno-0-4" name="__codelineno-0-4"></a> <span class="n">state</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">str</span><span class="p">]],</span>
<a href="#__codelineno-0-5" id="__codelineno-0-5" name="__codelineno-0-5"></a> <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">list</span><span class="p">[</span><span class="nb">str</span><span class="p">]]],</span>
<a href="#__codelineno-0-6" id="__codelineno-0-6" name="__codelineno-0-6"></a> <span class="n">cols</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">bool</span><span class="p">],</span>
<a href="#__codelineno-0-7" id="__codelineno-0-7" name="__codelineno-0-7"></a> <span class="n">diags1</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">bool</span><span class="p">],</span>
<a href="#__codelineno-0-8" id="__codelineno-0-8" name="__codelineno-0-8"></a> <span class="n">diags2</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">bool</span><span class="p">],</span>
<a href="#__codelineno-0-9" id="__codelineno-0-9" name="__codelineno-0-9"></a><span class="p">):</span>
<a href="#__codelineno-0-10" id="__codelineno-0-10" name="__codelineno-0-10"></a><span class="w"> </span><span class="sd">"""バックトラッキング:n クイーン"""</span>
<a href="#__codelineno-0-11" id="__codelineno-0-11" name="__codelineno-0-11"></a> <span class="c1"># すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-0-12" id="__codelineno-0-12" name="__codelineno-0-12"></a> <span class="k">if</span> <span class="n">row</span> <span class="o">==</span> <span class="n">n</span><span class="p">:</span>
<a href="#__codelineno-0-13" id="__codelineno-0-13" name="__codelineno-0-13"></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">row</span><span class="p">)</span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">state</span><span class="p">])</span>
<a href="#__codelineno-0-14" id="__codelineno-0-14" name="__codelineno-0-14"></a> <span class="k">return</span>
<a href="#__codelineno-0-15" id="__codelineno-0-15" name="__codelineno-0-15"></a> <span class="c1"># すべての列を走査する</span>
<a href="#__codelineno-0-16" id="__codelineno-0-16" name="__codelineno-0-16"></a> <span class="k">for</span> <span class="n">col</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">n</span><span class="p">):</span>
<a href="#__codelineno-0-17" id="__codelineno-0-17" name="__codelineno-0-17"></a> <span class="c1"># このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-0-18" id="__codelineno-0-18" name="__codelineno-0-18"></a> <span class="n">diag1</span> <span class="o">=</span> <span class="n">row</span> <span class="o">-</span> <span class="n">col</span> <span class="o">+</span> <span class="n">n</span> <span class="o">-</span> <span class="mi">1</span>
<a href="#__codelineno-0-19" id="__codelineno-0-19" name="__codelineno-0-19"></a> <span class="n">diag2</span> <span class="o">=</span> <span class="n">row</span> <span class="o">+</span> <span class="n">col</span>
<a href="#__codelineno-0-20" id="__codelineno-0-20" name="__codelineno-0-20"></a> <span class="c1"># 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-0-21" id="__codelineno-0-21" name="__codelineno-0-21"></a> <span class="k">if</span> <span class="ow">not</span> <span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span> <span class="ow">and</span> <span class="ow">not</span> <span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span> <span class="ow">and</span> <span class="ow">not</span> <span class="n">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">]:</span>
<a href="#__codelineno-0-22" id="__codelineno-0-22" name="__codelineno-0-22"></a> <span class="c1"># 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-0-23" id="__codelineno-0-23" name="__codelineno-0-23"></a> <span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"Q"</span>
<a href="#__codelineno-0-24" id="__codelineno-0-24" name="__codelineno-0-24"></a> <span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span> <span class="o">=</span> <span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span> <span class="o">=</span> <span class="n">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">]</span> <span class="o">=</span> <span class="kc">True</span>
<a href="#__codelineno-0-25" id="__codelineno-0-25" name="__codelineno-0-25"></a> <span class="c1"># 次の行に配置する</span>
<a href="#__codelineno-0-26" id="__codelineno-0-26" name="__codelineno-0-26"></a> <span class="n">backtrack</span><span class="p">(</span><span class="n">row</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">n</span><span class="p">,</span> <span class="n">state</span><span class="p">,</span> <span class="n">res</span><span class="p">,</span> <span class="n">cols</span><span class="p">,</span> <span class="n">diags1</span><span class="p">,</span> <span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-0-27" id="__codelineno-0-27" name="__codelineno-0-27"></a> <span class="c1"># 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-0-28" id="__codelineno-0-28" name="__codelineno-0-28"></a> <span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"#"</span>
<a href="#__codelineno-0-29" id="__codelineno-0-29" name="__codelineno-0-29"></a> <span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span> <span class="o">=</span> <span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span> <span class="o">=</span> <span class="n">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">]</span> <span class="o">=</span> <span class="kc">False</span>
<a href="#__codelineno-0-30" id="__codelineno-0-30" name="__codelineno-0-30"></a>
<a href="#__codelineno-0-31" id="__codelineno-0-31" name="__codelineno-0-31"></a><span class="k">def</span><span class="w"> </span><span class="nf">n_queens</span><span class="p">(</span><span class="n">n</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">list</span><span class="p">[</span><span class="nb">str</span><span class="p">]]]:</span>
<a href="#__codelineno-0-32" id="__codelineno-0-32" name="__codelineno-0-32"></a><span class="w"> </span><span class="sd">"""n クイーン問題を解く"""</span>
<a href="#__codelineno-0-33" id="__codelineno-0-33" name="__codelineno-0-33"></a> <span class="c1"># n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-0-34" id="__codelineno-0-34" name="__codelineno-0-34"></a> <span class="n">state</span> <span class="o">=</span> <span class="p">[[</span><span class="s2">"#"</span> <span class="k">for</span> <span class="n">_</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">n</span><span class="p">)]</span> <span class="k">for</span> <span class="n">_</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">n</span><span class="p">)]</span>
<a href="#__codelineno-0-35" id="__codelineno-0-35" name="__codelineno-0-35"></a> <span class="n">cols</span> <span class="o">=</span> <span class="p">[</span><span class="kc">False</span><span class="p">]</span> <span class="o">*</span> <span class="n">n</span> <span class="c1"># 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-0-36" id="__codelineno-0-36" name="__codelineno-0-36"></a> <span class="n">diags1</span> <span class="o">=</span> <span class="p">[</span><span class="kc">False</span><span class="p">]</span> <span class="o">*</span> <span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="n">n</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span> <span class="c1"># 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-0-37" id="__codelineno-0-37" name="__codelineno-0-37"></a> <span class="n">diags2</span> <span class="o">=</span> <span class="p">[</span><span class="kc">False</span><span class="p">]</span> <span class="o">*</span> <span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="n">n</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span> <span class="c1"># 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-0-38" id="__codelineno-0-38" name="__codelineno-0-38"></a> <span class="n">res</span> <span class="o">=</span> <span class="p">[]</span>
<a href="#__codelineno-0-39" id="__codelineno-0-39" name="__codelineno-0-39"></a> <span class="n">backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">n</span><span class="p">,</span> <span class="n">state</span><span class="p">,</span> <span class="n">res</span><span class="p">,</span> <span class="n">cols</span><span class="p">,</span> <span class="n">diags1</span><span class="p">,</span> <span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-0-40" id="__codelineno-0-40" name="__codelineno-0-40"></a>
<a href="#__codelineno-0-41" id="__codelineno-0-41" name="__codelineno-0-41"></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">n_queens.cpp</span><pre><span></span><code><a href="#__codelineno-1-1" id="__codelineno-1-1" name="__codelineno-1-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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="kt">int</span><span class="w"> </span><span class="n">row</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</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="n">string</span><span class="o">&gt;&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="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="n">string</span><span class="o">&gt;&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="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">cols</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="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">diags1</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">diags2</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-1-4" id="__codelineno-1-4" name="__codelineno-1-4"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-1-5" id="__codelineno-1-5" name="__codelineno-1-5"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </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="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-1-7" id="__codelineno-1-7" name="__codelineno-1-7"></a><span class="w"> </span><span class="k">return</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="p">}</span>
<a href="#__codelineno-1-9" id="__codelineno-1-9" name="__codelineno-1-9"></a><span class="w"> </span><span class="c1">// すべての列を走査する</span>
<a href="#__codelineno-1-10" id="__codelineno-1-10" name="__codelineno-1-10"></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">col</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">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">col</span><span class="o">++</span><span class="p">)</span><span class="w"> </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">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-1-12" id="__codelineno-1-12" name="__codelineno-1-12"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</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-1-13" id="__codelineno-1-13" name="__codelineno-1-13"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</span><span class="p">;</span>
<a href="#__codelineno-1-14" id="__codelineno-1-14" name="__codelineno-1-14"></a><span class="w"> </span><span class="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-1-15" id="__codelineno-1-15" name="__codelineno-1-15"></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">cols</span><span class="p">[</span><span class="n">col</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">diags1</span><span class="p">[</span><span class="n">diag1</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">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">])</span><span class="w"> </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">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-1-17" id="__codelineno-1-17" name="__codelineno-1-17"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Q"</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="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-1-19" id="__codelineno-1-19" name="__codelineno-1-19"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-1-20" id="__codelineno-1-20" name="__codelineno-1-20"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</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="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-1-22" id="__codelineno-1-22" name="__codelineno-1-22"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"#"</span><span class="p">;</span>
<a href="#__codelineno-1-23" id="__codelineno-1-23" name="__codelineno-1-23"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-1-24" id="__codelineno-1-24" name="__codelineno-1-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-1-25" id="__codelineno-1-25" name="__codelineno-1-25"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-1-26" id="__codelineno-1-26" name="__codelineno-1-26"></a><span class="p">}</span>
<a href="#__codelineno-1-27" id="__codelineno-1-27" name="__codelineno-1-27"></a>
<a href="#__codelineno-1-28" id="__codelineno-1-28" name="__codelineno-1-28"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-1-29" id="__codelineno-1-29" name="__codelineno-1-29"></a><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="n">vector</span><span class="o">&lt;</span><span class="n">string</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="n">nQueens</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </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="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-1-31" id="__codelineno-1-31" name="__codelineno-1-31"></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="n">string</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="n">string</span><span class="o">&gt;</span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="s">"#"</span><span class="p">));</span>
<a href="#__codelineno-1-32" id="__codelineno-1-32" name="__codelineno-1-32"></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">cols</span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="nb">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-1-33" id="__codelineno-1-33" name="__codelineno-1-33"></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">diags1</span><span class="p">(</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="nb">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-1-34" id="__codelineno-1-34" name="__codelineno-1-34"></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">diags2</span><span class="p">(</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="nb">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-1-35" id="__codelineno-1-35" name="__codelineno-1-35"></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="n">vector</span><span class="o">&lt;</span><span class="n">string</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
<a href="#__codelineno-1-36" id="__codelineno-1-36" name="__codelineno-1-36"></a>
<a href="#__codelineno-1-37" id="__codelineno-1-37" name="__codelineno-1-37"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-1-38" id="__codelineno-1-38" name="__codelineno-1-38"></a>
<a href="#__codelineno-1-39" id="__codelineno-1-39" name="__codelineno-1-39"></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-1-40" id="__codelineno-1-40" name="__codelineno-1-40"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.java</span><pre><span></span><code><a href="#__codelineno-2-1" id="__codelineno-2-1" name="__codelineno-2-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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="kt">int</span><span class="w"> </span><span class="n">row</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</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">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</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">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="n">res</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="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">cols</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">diags1</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">diags2</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-4" id="__codelineno-2-4" name="__codelineno-2-4"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-2-5" id="__codelineno-2-5" name="__codelineno-2-5"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </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="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">copyState</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;&gt;</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="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span><span class="w"> </span><span class="n">sRow</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">state</span><span class="p">)</span><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="n">copyState</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;&gt;</span><span class="p">(</span><span class="n">sRow</span><span class="p">));</span>
<a href="#__codelineno-2-9" id="__codelineno-2-9" name="__codelineno-2-9"></a><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="n">res</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">copyState</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="k">return</span><span class="p">;</span>
<a href="#__codelineno-2-12" id="__codelineno-2-12" name="__codelineno-2-12"></a><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">// すべての列を走査する</span>
<a href="#__codelineno-2-14" id="__codelineno-2-14" name="__codelineno-2-14"></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">col</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">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">col</span><span class="o">++</span><span class="p">)</span><span class="w"> </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="c1">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-2-16" id="__codelineno-2-16" name="__codelineno-2-16"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</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-2-17" id="__codelineno-2-17" name="__codelineno-2-17"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</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">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-2-19" id="__codelineno-2-19" name="__codelineno-2-19"></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">cols</span><span class="o">[</span><span class="n">col</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">diags1</span><span class="o">[</span><span class="n">diag1</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">diags2</span><span class="o">[</span><span class="n">diag2</span><span class="o">]</span><span class="p">)</span><span class="w"> </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="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-2-21" id="__codelineno-2-21" name="__codelineno-2-21"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">get</span><span class="p">(</span><span class="n">row</span><span class="p">).</span><span class="na">set</span><span class="p">(</span><span class="n">col</span><span class="p">,</span><span class="w"> </span><span class="s">"Q"</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="n">cols</span><span class="o">[</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</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-2-23" id="__codelineno-2-23" name="__codelineno-2-23"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-2-24" id="__codelineno-2-24" name="__codelineno-2-24"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-2-25" id="__codelineno-2-25" name="__codelineno-2-25"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-2-26" id="__codelineno-2-26" name="__codelineno-2-26"></a><span class="w"> </span><span class="n">state</span><span class="p">.</span><span class="na">get</span><span class="p">(</span><span class="n">row</span><span class="p">).</span><span class="na">set</span><span class="p">(</span><span class="n">col</span><span class="p">,</span><span class="w"> </span><span class="s">"#"</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">cols</span><span class="o">[</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</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-2-28" id="__codelineno-2-28" name="__codelineno-2-28"></a><span class="w"> </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="p">}</span>
<a href="#__codelineno-2-30" id="__codelineno-2-30" name="__codelineno-2-30"></a><span class="p">}</span>
<a href="#__codelineno-2-31" id="__codelineno-2-31" name="__codelineno-2-31"></a>
<a href="#__codelineno-2-32" id="__codelineno-2-32" name="__codelineno-2-32"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-2-33" id="__codelineno-2-33" name="__codelineno-2-33"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="nf">nQueens</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-34" id="__codelineno-2-34" name="__codelineno-2-34"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-2-35" id="__codelineno-2-35" name="__codelineno-2-35"></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">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</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;&gt;</span><span class="p">();</span>
<a href="#__codelineno-2-36" id="__codelineno-2-36" name="__codelineno-2-36"></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">n</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-2-37" id="__codelineno-2-37" name="__codelineno-2-37"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span><span class="w"> </span><span class="n">row</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;&gt;</span><span class="p">();</span>
<a href="#__codelineno-2-38" id="__codelineno-2-38" name="__codelineno-2-38"></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">j</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">j</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">j</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-2-39" id="__codelineno-2-39" name="__codelineno-2-39"></a><span class="w"> </span><span class="n">row</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="s">"#"</span><span class="p">);</span>
<a href="#__codelineno-2-40" id="__codelineno-2-40" name="__codelineno-2-40"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-2-41" id="__codelineno-2-41" name="__codelineno-2-41"></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">row</span><span class="p">);</span>
<a href="#__codelineno-2-42" id="__codelineno-2-42" name="__codelineno-2-42"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-2-43" id="__codelineno-2-43" name="__codelineno-2-43"></a><span class="w"> </span><span class="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">cols</span><span class="w"> </span><span class="o">=</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">n</span><span class="o">]</span><span class="p">;</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-2-44" id="__codelineno-2-44" name="__codelineno-2-44"></a><span class="w"> </span><span class="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">diags1</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="p">;</span><span class="w"> </span><span class="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-2-45" id="__codelineno-2-45" name="__codelineno-2-45"></a><span class="w"> </span><span class="kt">boolean</span><span class="o">[]</span><span class="w"> </span><span class="n">diags2</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="p">;</span><span class="w"> </span><span class="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-2-46" id="__codelineno-2-46" name="__codelineno-2-46"></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">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;&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;&gt;</span><span class="p">();</span>
<a href="#__codelineno-2-47" id="__codelineno-2-47" name="__codelineno-2-47"></a>
<a href="#__codelineno-2-48" id="__codelineno-2-48" name="__codelineno-2-48"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-2-49" id="__codelineno-2-49" name="__codelineno-2-49"></a>
<a href="#__codelineno-2-50" id="__codelineno-2-50" name="__codelineno-2-50"></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-2-51" id="__codelineno-2-51" name="__codelineno-2-51"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.cs</span><pre><span></span><code><a href="#__codelineno-3-1" id="__codelineno-3-1" name="__codelineno-3-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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="kt">int</span><span class="w"> </span><span class="n">row</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</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">string</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</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">List</span><span class="o">&lt;</span><span class="kt">string</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="n">res</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="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">cols</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">diags1</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">diags2</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-4" id="__codelineno-3-4" name="__codelineno-3-4"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-3-5" id="__codelineno-3-5" name="__codelineno-3-5"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </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="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">string</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">copyState</span><span class="w"> </span><span class="o">=</span><span class="w"> </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="k">foreach</span><span class="w"> </span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">string</span><span class="o">&gt;</span><span class="w"> </span><span class="n">sRow</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">state</span><span class="p">)</span><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="n">copyState</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">string</span><span class="o">&gt;</span><span class="p">(</span><span class="n">sRow</span><span class="p">));</span>
<a href="#__codelineno-3-9" id="__codelineno-3-9" name="__codelineno-3-9"></a><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="n">res</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="n">copyState</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="k">return</span><span class="p">;</span>
<a href="#__codelineno-3-12" id="__codelineno-3-12" name="__codelineno-3-12"></a><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">// すべての列を走査する</span>
<a href="#__codelineno-3-14" id="__codelineno-3-14" name="__codelineno-3-14"></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">col</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">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">col</span><span class="o">++</span><span class="p">)</span><span class="w"> </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="c1">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-3-16" id="__codelineno-3-16" name="__codelineno-3-16"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</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-3-17" id="__codelineno-3-17" name="__codelineno-3-17"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</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">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-3-19" id="__codelineno-3-19" name="__codelineno-3-19"></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">cols</span><span class="p">[</span><span class="n">col</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">diags1</span><span class="p">[</span><span class="n">diag1</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">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">])</span><span class="w"> </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="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-3-21" id="__codelineno-3-21" name="__codelineno-3-21"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Q"</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="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-3-23" id="__codelineno-3-23" name="__codelineno-3-23"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-3-24" id="__codelineno-3-24" name="__codelineno-3-24"></a><span class="w"> </span><span class="n">Backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-3-25" id="__codelineno-3-25" name="__codelineno-3-25"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-3-26" id="__codelineno-3-26" name="__codelineno-3-26"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"#"</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">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-3-28" id="__codelineno-3-28" name="__codelineno-3-28"></a><span class="w"> </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="p">}</span>
<a href="#__codelineno-3-30" id="__codelineno-3-30" name="__codelineno-3-30"></a><span class="p">}</span>
<a href="#__codelineno-3-31" id="__codelineno-3-31" name="__codelineno-3-31"></a>
<a href="#__codelineno-3-32" id="__codelineno-3-32" name="__codelineno-3-32"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-3-33" id="__codelineno-3-33" name="__codelineno-3-33"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">string</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="n">NQueens</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-34" id="__codelineno-3-34" name="__codelineno-3-34"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-3-35" id="__codelineno-3-35" name="__codelineno-3-35"></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">string</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-3-36" id="__codelineno-3-36" name="__codelineno-3-36"></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">n</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-3-37" id="__codelineno-3-37" name="__codelineno-3-37"></a><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">string</span><span class="o">&gt;</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-3-38" id="__codelineno-3-38" name="__codelineno-3-38"></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">j</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">j</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">j</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-3-39" id="__codelineno-3-39" name="__codelineno-3-39"></a><span class="w"> </span><span class="n">row</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="s">"#"</span><span class="p">);</span>
<a href="#__codelineno-3-40" id="__codelineno-3-40" name="__codelineno-3-40"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-3-41" id="__codelineno-3-41" name="__codelineno-3-41"></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">row</span><span class="p">);</span>
<a href="#__codelineno-3-42" id="__codelineno-3-42" name="__codelineno-3-42"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-3-43" id="__codelineno-3-43" name="__codelineno-3-43"></a><span class="w"> </span><span class="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">cols</span><span class="w"> </span><span class="o">=</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">n</span><span class="p">];</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-3-44" id="__codelineno-3-44" name="__codelineno-3-44"></a><span class="w"> </span><span class="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">diags1</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-3-45" id="__codelineno-3-45" name="__codelineno-3-45"></a><span class="w"> </span><span class="kt">bool</span><span class="p">[]</span><span class="w"> </span><span class="n">diags2</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-3-46" id="__codelineno-3-46" name="__codelineno-3-46"></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">List</span><span class="o">&lt;</span><span class="kt">string</span><span class="o">&gt;&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-3-47" id="__codelineno-3-47" name="__codelineno-3-47"></a>
<a href="#__codelineno-3-48" id="__codelineno-3-48" name="__codelineno-3-48"></a><span class="w"> </span><span class="n">Backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-3-49" id="__codelineno-3-49" name="__codelineno-3-49"></a>
<a href="#__codelineno-3-50" id="__codelineno-3-50" name="__codelineno-3-50"></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-3-51" id="__codelineno-3-51" name="__codelineno-3-51"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.go</span><pre><span></span><code><a href="#__codelineno-4-1" id="__codelineno-4-1" name="__codelineno-4-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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">backtrack</span><span class="p">(</span><span class="nx">row</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="w"> </span><span class="o">*</span><span class="p">[][]</span><span class="kt">string</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">string</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</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="p">{</span>
<a href="#__codelineno-4-3" id="__codelineno-4-3" name="__codelineno-4-3"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</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="nx">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nx">n</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">make</span><span class="p">([][]</span><span class="kt">string</span><span class="p">,</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>
<a href="#__codelineno-4-6" id="__codelineno-4-6" name="__codelineno-4-6"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">i</span><span class="p">,</span><span class="w"> </span><span class="nx">_</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">range</span><span class="w"> </span><span class="nx">newState</span><span class="w"> </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="nx">newState</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="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</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="mi">0</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="nb">copy</span><span class="p">(</span><span class="nx">newState</span><span class="p">[</span><span class="nx">i</span><span class="p">],</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)[</span><span class="nx">i</span><span class="p">])</span>
<a href="#__codelineno-4-9" id="__codelineno-4-9" name="__codelineno-4-9"></a>
<a href="#__codelineno-4-10" id="__codelineno-4-10" name="__codelineno-4-10"></a><span class="w"> </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="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-4-12" id="__codelineno-4-12" name="__codelineno-4-12"></a><span class="w"> </span><span class="k">return</span>
<a href="#__codelineno-4-13" id="__codelineno-4-13" name="__codelineno-4-13"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-4-14" id="__codelineno-4-14" name="__codelineno-4-14"></a><span class="w"> </span><span class="c1">// すべての列を走査する</span>
<a href="#__codelineno-4-15" id="__codelineno-4-15" name="__codelineno-4-15"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">col</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">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="nx">n</span><span class="p">;</span><span class="w"> </span><span class="nx">col</span><span class="o">++</span><span class="w"> </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">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-4-17" id="__codelineno-4-17" name="__codelineno-4-17"></a><span class="w"> </span><span class="nx">diag1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span>
<a href="#__codelineno-4-18" id="__codelineno-4-18" name="__codelineno-4-18"></a><span class="w"> </span><span class="nx">diag2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">col</span>
<a href="#__codelineno-4-19" id="__codelineno-4-19" name="__codelineno-4-19"></a><span class="w"> </span><span class="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-4-20" id="__codelineno-4-20" name="__codelineno-4-20"></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">cols</span><span class="p">)[</span><span class="nx">col</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="p">(</span><span class="o">*</span><span class="nx">diags1</span><span class="p">)[</span><span class="nx">diag1</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="p">(</span><span class="o">*</span><span class="nx">diags2</span><span class="p">)[</span><span class="nx">diag2</span><span class="p">]</span><span class="w"> </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="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-4-22" id="__codelineno-4-22" name="__codelineno-4-22"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)[</span><span class="nx">row</span><span class="p">][</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Q"</span>
<a href="#__codelineno-4-23" id="__codelineno-4-23" name="__codelineno-4-23"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">cols</span><span class="p">)[</span><span class="nx">col</span><span class="p">],</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">diags1</span><span class="p">)[</span><span class="nx">diag1</span><span class="p">],</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">diags2</span><span class="p">)[</span><span class="nx">diag2</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><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w"> </span><span class="kc">true</span>
<a href="#__codelineno-4-24" id="__codelineno-4-24" name="__codelineno-4-24"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-4-25" id="__codelineno-4-25" name="__codelineno-4-25"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">row</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</span><span class="p">)</span>
<a href="#__codelineno-4-26" id="__codelineno-4-26" name="__codelineno-4-26"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-4-27" id="__codelineno-4-27" name="__codelineno-4-27"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">state</span><span class="p">)[</span><span class="nx">row</span><span class="p">][</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"#"</span>
<a href="#__codelineno-4-28" id="__codelineno-4-28" name="__codelineno-4-28"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">cols</span><span class="p">)[</span><span class="nx">col</span><span class="p">],</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">diags1</span><span class="p">)[</span><span class="nx">diag1</span><span class="p">],</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="nx">diags2</span><span class="p">)[</span><span class="nx">diag2</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><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span>
<a href="#__codelineno-4-29" id="__codelineno-4-29" name="__codelineno-4-29"></a><span class="w"> </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="p">}</span>
<a href="#__codelineno-4-31" id="__codelineno-4-31" name="__codelineno-4-31"></a><span class="p">}</span>
<a href="#__codelineno-4-32" id="__codelineno-4-32" name="__codelineno-4-32"></a>
<a href="#__codelineno-4-33" id="__codelineno-4-33" name="__codelineno-4-33"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-4-34" id="__codelineno-4-34" name="__codelineno-4-34"></a><span class="kd">func</span><span class="w"> </span><span class="nx">nQueens</span><span class="p">(</span><span class="nx">n</span><span class="w"> </span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="p">[][][]</span><span class="kt">string</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-4-35" id="__codelineno-4-35" name="__codelineno-4-35"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-4-36" id="__codelineno-4-36" name="__codelineno-4-36"></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">string</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">)</span>
<a href="#__codelineno-4-37" id="__codelineno-4-37" name="__codelineno-4-37"></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="nx">n</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-4-38" id="__codelineno-4-38" name="__codelineno-4-38"></a><span class="w"> </span><span class="nx">row</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">string</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">)</span>
<a href="#__codelineno-4-39" id="__codelineno-4-39" name="__codelineno-4-39"></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="nx">n</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-4-40" id="__codelineno-4-40" name="__codelineno-4-40"></a><span class="w"> </span><span class="nx">row</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="s">"#"</span>
<a href="#__codelineno-4-41" id="__codelineno-4-41" name="__codelineno-4-41"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-4-42" id="__codelineno-4-42" name="__codelineno-4-42"></a><span class="w"> </span><span class="nx">state</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="nx">row</span>
<a href="#__codelineno-4-43" id="__codelineno-4-43" name="__codelineno-4-43"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-4-44" id="__codelineno-4-44" name="__codelineno-4-44"></a><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-4-45" id="__codelineno-4-45" name="__codelineno-4-45"></a><span class="w"> </span><span class="nx">cols</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="nx">n</span><span class="p">)</span>
<a href="#__codelineno-4-46" id="__codelineno-4-46" name="__codelineno-4-46"></a><span class="w"> </span><span class="nx">diags1</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="mi">2</span><span class="o">*</span><span class="nx">n</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<a href="#__codelineno-4-47" id="__codelineno-4-47" name="__codelineno-4-47"></a><span class="w"> </span><span class="nx">diags2</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="mi">2</span><span class="o">*</span><span class="nx">n</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<a href="#__codelineno-4-48" id="__codelineno-4-48" name="__codelineno-4-48"></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">string</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
<a href="#__codelineno-4-49" id="__codelineno-4-49" name="__codelineno-4-49"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </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">res</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="nx">diags2</span><span class="p">)</span>
<a href="#__codelineno-4-50" id="__codelineno-4-50" name="__codelineno-4-50"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">res</span>
<a href="#__codelineno-4-51" id="__codelineno-4-51" name="__codelineno-4-51"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.swift</span><pre><span></span><code><a href="#__codelineno-5-1" id="__codelineno-5-1" name="__codelineno-5-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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">row</span><span class="p">:</span><span class="w"> </span><span class="nb">Int</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">:</span><span class="w"> </span><span class="nb">Int</span><span class="p">,</span><span class="w"> </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">String</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">String</span><span class="p">]]],</span><span class="w"> </span><span class="n">cols</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">diags1</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">diags2</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="p">{</span>
<a href="#__codelineno-5-3" id="__codelineno-5-3" name="__codelineno-5-3"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</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">row</span><span class="w"> </span><span class="p">==</span><span class="w"> </span><span class="n">n</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">// すべての列を走査する</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="n">col</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">..</span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</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">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-5-11" id="__codelineno-5-11" name="__codelineno-5-11"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="nv">diag1</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span>
<a href="#__codelineno-5-12" id="__codelineno-5-12" name="__codelineno-5-12"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="nv">diag2</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</span>
<a href="#__codelineno-5-13" id="__codelineno-5-13" name="__codelineno-5-13"></a><span class="w"> </span><span class="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-5-14" id="__codelineno-5-14" name="__codelineno-5-14"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">cols</span><span class="p">[</span><span class="n">col</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">diags1</span><span class="p">[</span><span class="n">diag1</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">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">]</span><span class="w"> </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">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-5-16" id="__codelineno-5-16" name="__codelineno-5-16"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="s">"Q"</span>
<a href="#__codelineno-5-17" id="__codelineno-5-17" name="__codelineno-5-17"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</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-5-18" id="__codelineno-5-18" name="__codelineno-5-18"></a><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</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-5-19" id="__codelineno-5-19" name="__codelineno-5-19"></a><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-5-20" id="__codelineno-5-20" name="__codelineno-5-20"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-5-21" id="__codelineno-5-21" name="__codelineno-5-21"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</span><span class="p">:</span><span class="w"> </span><span class="n">row</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">n</span><span class="p">:</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </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">res</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">cols</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-5-22" id="__codelineno-5-22" name="__codelineno-5-22"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-5-23" id="__codelineno-5-23" name="__codelineno-5-23"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="s">"#"</span>
<a href="#__codelineno-5-24" id="__codelineno-5-24" name="__codelineno-5-24"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</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-5-25" id="__codelineno-5-25" name="__codelineno-5-25"></a><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</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-5-26" id="__codelineno-5-26" name="__codelineno-5-26"></a><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-5-27" id="__codelineno-5-27" name="__codelineno-5-27"></a><span class="w"> </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="p">}</span>
<a href="#__codelineno-5-29" id="__codelineno-5-29" name="__codelineno-5-29"></a><span class="p">}</span>
<a href="#__codelineno-5-30" id="__codelineno-5-30" name="__codelineno-5-30"></a>
<a href="#__codelineno-5-31" id="__codelineno-5-31" name="__codelineno-5-31"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-5-32" id="__codelineno-5-32" name="__codelineno-5-32"></a><span class="kd">func</span><span class="w"> </span><span class="nf">nQueens</span><span class="p">(</span><span class="n">n</span><span class="p">:</span><span class="w"> </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">String</span><span class="p">]]]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-5-33" id="__codelineno-5-33" name="__codelineno-5-33"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-5-34" id="__codelineno-5-34" name="__codelineno-5-34"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">state</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="nb">Array</span><span class="p">(</span><span class="n">repeating</span><span class="p">:</span><span class="w"> </span><span class="s">"#"</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">n</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">n</span><span class="p">)</span>
<a href="#__codelineno-5-35" id="__codelineno-5-35" name="__codelineno-5-35"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">cols</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">n</span><span class="p">)</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-5-36" id="__codelineno-5-36" name="__codelineno-5-36"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">diags1</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-5-37" id="__codelineno-5-37" name="__codelineno-5-37"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="nv">diags2</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-5-38" id="__codelineno-5-38" name="__codelineno-5-38"></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">String</span><span class="p">]]]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[]</span>
<a href="#__codelineno-5-39" id="__codelineno-5-39" name="__codelineno-5-39"></a>
<a href="#__codelineno-5-40" id="__codelineno-5-40" name="__codelineno-5-40"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">:</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </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">res</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">cols</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">:</span><span class="w"> </span><span class="p">&amp;</span><span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-5-41" id="__codelineno-5-41" name="__codelineno-5-41"></a>
<a href="#__codelineno-5-42" id="__codelineno-5-42" name="__codelineno-5-42"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-5-43" id="__codelineno-5-43" name="__codelineno-5-43"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.js</span><pre><span></span><code><a href="#__codelineno-6-1" id="__codelineno-6-1" name="__codelineno-6-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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">row</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</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">// すべての行への配置が終わったら、解を記録する</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">row</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="nx">n</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><span class="nx">map</span><span class="p">((</span><span class="nx">row</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nx">row</span><span class="p">.</span><span class="nx">slice</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">// すべての列を走査する</span>
<a href="#__codelineno-6-9" id="__codelineno-6-9" name="__codelineno-6-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kd">let</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0</span><span class="p">;</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="nx">n</span><span class="p">;</span><span class="w"> </span><span class="nx">col</span><span class="o">++</span><span class="p">)</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">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-6-11" id="__codelineno-6-11" name="__codelineno-6-11"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</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="kd">const</span><span class="w"> </span><span class="nx">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">col</span><span class="p">;</span>
<a href="#__codelineno-6-13" id="__codelineno-6-13" name="__codelineno-6-13"></a><span class="w"> </span><span class="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-6-14" id="__codelineno-6-14" name="__codelineno-6-14"></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">cols</span><span class="p">[</span><span class="nx">col</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">diags1</span><span class="p">[</span><span class="nx">diag1</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">diags2</span><span class="p">[</span><span class="nx">diag2</span><span class="p">])</span><span class="w"> </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">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-6-16" id="__codelineno-6-16" name="__codelineno-6-16"></a><span class="w"> </span><span class="nx">state</span><span class="p">[</span><span class="nx">row</span><span class="p">][</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'Q'</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="nx">cols</span><span class="p">[</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags1</span><span class="p">[</span><span class="nx">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags2</span><span class="p">[</span><span class="nx">diag2</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-6-18" id="__codelineno-6-18" name="__codelineno-6-18"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-6-19" id="__codelineno-6-19" name="__codelineno-6-19"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mf">1</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</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="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-6-21" id="__codelineno-6-21" name="__codelineno-6-21"></a><span class="w"> </span><span class="nx">state</span><span class="p">[</span><span class="nx">row</span><span class="p">][</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'#'</span><span class="p">;</span>
<a href="#__codelineno-6-22" id="__codelineno-6-22" name="__codelineno-6-22"></a><span class="w"> </span><span class="nx">cols</span><span class="p">[</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags1</span><span class="p">[</span><span class="nx">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags2</span><span class="p">[</span><span class="nx">diag2</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-6-23" id="__codelineno-6-23" name="__codelineno-6-23"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-6-24" id="__codelineno-6-24" name="__codelineno-6-24"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-6-25" id="__codelineno-6-25" name="__codelineno-6-25"></a><span class="p">}</span>
<a href="#__codelineno-6-26" id="__codelineno-6-26" name="__codelineno-6-26"></a>
<a href="#__codelineno-6-27" id="__codelineno-6-27" name="__codelineno-6-27"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-6-28" id="__codelineno-6-28" name="__codelineno-6-28"></a><span class="kd">function</span><span class="w"> </span><span class="nx">nQueens</span><span class="p">(</span><span class="nx">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-6-29" id="__codelineno-6-29" name="__codelineno-6-29"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-6-30" id="__codelineno-6-30" name="__codelineno-6-30"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">.</span><span class="kr">from</span><span class="p">({</span><span class="w"> </span><span class="nx">length</span><span class="o">:</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="p">},</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">n</span><span class="p">).</span><span class="nx">fill</span><span class="p">(</span><span class="s1">'#'</span><span class="p">));</span>
<a href="#__codelineno-6-31" id="__codelineno-6-31" name="__codelineno-6-31"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">cols</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">n</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="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-6-32" id="__codelineno-6-32" name="__codelineno-6-32"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">diags1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="mf">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</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="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-6-33" id="__codelineno-6-33" name="__codelineno-6-33"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">diags2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="mf">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</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="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-6-34" id="__codelineno-6-34" name="__codelineno-6-34"></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-6-35" id="__codelineno-6-35" name="__codelineno-6-35"></a>
<a href="#__codelineno-6-36" id="__codelineno-6-36" name="__codelineno-6-36"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="mf">0</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</span><span class="p">);</span>
<a href="#__codelineno-6-37" id="__codelineno-6-37" name="__codelineno-6-37"></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-6-38" id="__codelineno-6-38" name="__codelineno-6-38"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.ts</span><pre><span></span><code><a href="#__codelineno-7-1" id="__codelineno-7-1" name="__codelineno-7-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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">row</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">n</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">state</span><span class="o">:</span><span class="w"> </span><span class="kt">string</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">string</span><span class="p">[][][],</span>
<a href="#__codelineno-7-7" id="__codelineno-7-7" name="__codelineno-7-7"></a><span class="w"> </span><span class="nx">cols</span><span class="o">:</span><span class="w"> </span><span class="kt">boolean</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="nx">diags1</span><span class="o">:</span><span class="w"> </span><span class="kt">boolean</span><span class="p">[],</span>
<a href="#__codelineno-7-9" id="__codelineno-7-9" name="__codelineno-7-9"></a><span class="w"> </span><span class="nx">diags2</span><span class="o">:</span><span class="w"> </span><span class="kt">boolean</span><span class="p">[]</span>
<a href="#__codelineno-7-10" id="__codelineno-7-10" name="__codelineno-7-10"></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-7-11" id="__codelineno-7-11" name="__codelineno-7-11"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-7-12" id="__codelineno-7-12" name="__codelineno-7-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">row</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="nx">n</span><span class="p">)</span><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="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><span class="nx">map</span><span class="p">((</span><span class="nx">row</span><span class="p">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nx">row</span><span class="p">.</span><span class="nx">slice</span><span class="p">()));</span>
<a href="#__codelineno-7-14" id="__codelineno-7-14" name="__codelineno-7-14"></a><span class="w"> </span><span class="k">return</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="p">}</span>
<a href="#__codelineno-7-16" id="__codelineno-7-16" name="__codelineno-7-16"></a><span class="w"> </span><span class="c1">// すべての列を走査する</span>
<a href="#__codelineno-7-17" id="__codelineno-7-17" name="__codelineno-7-17"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kd">let</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0</span><span class="p">;</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="nx">n</span><span class="p">;</span><span class="w"> </span><span class="nx">col</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-18" id="__codelineno-7-18" name="__codelineno-7-18"></a><span class="w"> </span><span class="c1">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-7-19" id="__codelineno-7-19" name="__codelineno-7-19"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</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="kd">const</span><span class="w"> </span><span class="nx">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">col</span><span class="p">;</span>
<a href="#__codelineno-7-21" id="__codelineno-7-21" name="__codelineno-7-21"></a><span class="w"> </span><span class="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-7-22" id="__codelineno-7-22" name="__codelineno-7-22"></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">cols</span><span class="p">[</span><span class="nx">col</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">diags1</span><span class="p">[</span><span class="nx">diag1</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">diags2</span><span class="p">[</span><span class="nx">diag2</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-23" id="__codelineno-7-23" name="__codelineno-7-23"></a><span class="w"> </span><span class="c1">// 試行:このマスにクイーンを配置する</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">row</span><span class="p">][</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'Q'</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="nx">cols</span><span class="p">[</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags1</span><span class="p">[</span><span class="nx">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags2</span><span class="p">[</span><span class="nx">diag2</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-7-26" id="__codelineno-7-26" name="__codelineno-7-26"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-7-27" id="__codelineno-7-27" name="__codelineno-7-27"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="nx">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mf">1</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</span><span class="p">);</span>
<a href="#__codelineno-7-28" id="__codelineno-7-28" name="__codelineno-7-28"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-7-29" id="__codelineno-7-29" name="__codelineno-7-29"></a><span class="w"> </span><span class="nx">state</span><span class="p">[</span><span class="nx">row</span><span class="p">][</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'#'</span><span class="p">;</span>
<a href="#__codelineno-7-30" id="__codelineno-7-30" name="__codelineno-7-30"></a><span class="w"> </span><span class="nx">cols</span><span class="p">[</span><span class="nx">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags1</span><span class="p">[</span><span class="nx">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">diags2</span><span class="p">[</span><span class="nx">diag2</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-7-31" id="__codelineno-7-31" name="__codelineno-7-31"></a><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="p">}</span>
<a href="#__codelineno-7-33" id="__codelineno-7-33" name="__codelineno-7-33"></a><span class="p">}</span>
<a href="#__codelineno-7-34" id="__codelineno-7-34" name="__codelineno-7-34"></a>
<a href="#__codelineno-7-35" id="__codelineno-7-35" name="__codelineno-7-35"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-7-36" id="__codelineno-7-36" name="__codelineno-7-36"></a><span class="kd">function</span><span class="w"> </span><span class="nx">nQueens</span><span class="p">(</span><span class="nx">n</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">string</span><span class="p">[][][]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-7-37" id="__codelineno-7-37" name="__codelineno-7-37"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-7-38" id="__codelineno-7-38" name="__codelineno-7-38"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">.</span><span class="kr">from</span><span class="p">({</span><span class="w"> </span><span class="nx">length</span><span class="o">:</span><span class="w"> </span><span class="kt">n</span><span class="w"> </span><span class="p">},</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">n</span><span class="p">).</span><span class="nx">fill</span><span class="p">(</span><span class="s1">'#'</span><span class="p">));</span>
<a href="#__codelineno-7-39" id="__codelineno-7-39" name="__codelineno-7-39"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">cols</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="nx">n</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="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-7-40" id="__codelineno-7-40" name="__codelineno-7-40"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">diags1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="mf">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</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="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-7-41" id="__codelineno-7-41" name="__codelineno-7-41"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">diags2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">Array</span><span class="p">(</span><span class="mf">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</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="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-7-42" id="__codelineno-7-42" name="__codelineno-7-42"></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">string</span><span class="p">[][][]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
<a href="#__codelineno-7-43" id="__codelineno-7-43" name="__codelineno-7-43"></a>
<a href="#__codelineno-7-44" id="__codelineno-7-44" name="__codelineno-7-44"></a><span class="w"> </span><span class="nx">backtrack</span><span class="p">(</span><span class="mf">0</span><span class="p">,</span><span class="w"> </span><span class="nx">n</span><span class="p">,</span><span class="w"> </span><span class="nx">state</span><span class="p">,</span><span class="w"> </span><span class="nx">res</span><span class="p">,</span><span class="w"> </span><span class="nx">cols</span><span class="p">,</span><span class="w"> </span><span class="nx">diags1</span><span class="p">,</span><span class="w"> </span><span class="nx">diags2</span><span class="p">);</span>
<a href="#__codelineno-7-45" id="__codelineno-7-45" name="__codelineno-7-45"></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-7-46" id="__codelineno-7-46" name="__codelineno-7-46"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.dart</span><pre><span></span><code><a href="#__codelineno-8-1" id="__codelineno-8-1" name="__codelineno-8-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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="kt">int</span><span class="w"> </span><span class="n">row</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="kt">int</span><span class="w"> </span><span class="n">n</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="n">List</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</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="n">List</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&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="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">cols</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="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">diags1</span><span class="p">,</span>
<a href="#__codelineno-8-9" id="__codelineno-8-9" name="__codelineno-8-9"></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">diags2</span><span class="p">,</span>
<a href="#__codelineno-8-10" id="__codelineno-8-10" name="__codelineno-8-10"></a><span class="p">)</span><span class="w"> </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="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-8-12" id="__codelineno-8-12" name="__codelineno-8-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><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="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">copyState</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</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="n">List</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;</span><span class="w"> </span><span class="n">sRow</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">state</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="n">copyState</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">sRow</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="p">}</span>
<a href="#__codelineno-8-17" id="__codelineno-8-17" name="__codelineno-8-17"></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">copyState</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="k">return</span><span class="p">;</span>
<a href="#__codelineno-8-19" id="__codelineno-8-19" name="__codelineno-8-19"></a><span class="w"> </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="c1">// すべての列を走査する</span>
<a href="#__codelineno-8-21" id="__codelineno-8-21" name="__codelineno-8-21"></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">col</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">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">col</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-22" id="__codelineno-8-22" name="__codelineno-8-22"></a><span class="w"> </span><span class="c1">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-8-23" id="__codelineno-8-23" name="__codelineno-8-23"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</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-8-24" id="__codelineno-8-24" name="__codelineno-8-24"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</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="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-8-26" id="__codelineno-8-26" name="__codelineno-8-26"></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">cols</span><span class="p">[</span><span class="n">col</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">diags1</span><span class="p">[</span><span class="n">diag1</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">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">])</span><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="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-8-28" id="__codelineno-8-28" name="__codelineno-8-28"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">"Q"</span><span class="p">;</span>
<a href="#__codelineno-8-29" id="__codelineno-8-29" name="__codelineno-8-29"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</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-8-30" id="__codelineno-8-30" name="__codelineno-8-30"></a><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</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-8-31" id="__codelineno-8-31" name="__codelineno-8-31"></a><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-8-32" id="__codelineno-8-32" name="__codelineno-8-32"></a><span class="w"> </span><span class="c1">// 次の行に配置する</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="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="m">1</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</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="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-8-35" id="__codelineno-8-35" name="__codelineno-8-35"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">"#"</span><span class="p">;</span>
<a href="#__codelineno-8-36" id="__codelineno-8-36" name="__codelineno-8-36"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</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-8-37" id="__codelineno-8-37" name="__codelineno-8-37"></a><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</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-8-38" id="__codelineno-8-38" name="__codelineno-8-38"></a><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-8-39" id="__codelineno-8-39" name="__codelineno-8-39"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-8-40" id="__codelineno-8-40" name="__codelineno-8-40"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-8-41" id="__codelineno-8-41" name="__codelineno-8-41"></a><span class="p">}</span>
<a href="#__codelineno-8-42" id="__codelineno-8-42" name="__codelineno-8-42"></a>
<a href="#__codelineno-8-43" id="__codelineno-8-43" name="__codelineno-8-43"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-8-44" id="__codelineno-8-44" name="__codelineno-8-44"></a><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="n">nQueens</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-8-45" id="__codelineno-8-45" name="__codelineno-8-45"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-8-46" id="__codelineno-8-46" name="__codelineno-8-46"></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">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="n">state</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">generate</span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="n">index</span><span class="p">)</span><span class="w"> </span><span class="o">=&gt;</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">n</span><span class="p">,</span><span class="w"> </span><span class="s2">"#"</span><span class="p">));</span>
<a href="#__codelineno-8-47" id="__codelineno-8-47" name="__codelineno-8-47"></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">cols</span><span class="w"> </span><span class="o">=</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">n</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-8-48" id="__codelineno-8-48" name="__codelineno-8-48"></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">diags1</span><span class="w"> </span><span class="o">=</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="m">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-8-49" id="__codelineno-8-49" name="__codelineno-8-49"></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">diags2</span><span class="w"> </span><span class="o">=</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="m">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-8-50" id="__codelineno-8-50" name="__codelineno-8-50"></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">List</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&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-8-51" id="__codelineno-8-51" name="__codelineno-8-51"></a>
<a href="#__codelineno-8-52" id="__codelineno-8-52" name="__codelineno-8-52"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="m">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-8-53" id="__codelineno-8-53" name="__codelineno-8-53"></a>
<a href="#__codelineno-8-54" id="__codelineno-8-54" name="__codelineno-8-54"></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-8-55" id="__codelineno-8-55" name="__codelineno-8-55"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.rs</span><pre><span></span><code><a href="#__codelineno-9-1" id="__codelineno-9-1" name="__codelineno-9-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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>
<a href="#__codelineno-9-3" id="__codelineno-9-3" name="__codelineno-9-3"></a><span class="w"> </span><span class="n">row</span><span class="p">:</span><span class="w"> </span><span class="kt">usize</span><span class="p">,</span>
<a href="#__codelineno-9-4" id="__codelineno-9-4" name="__codelineno-9-4"></a><span class="w"> </span><span class="n">n</span><span class="p">:</span><span class="w"> </span><span class="kt">usize</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">state</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="nb">String</span><span class="o">&gt;&gt;</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="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="nb">Vec</span><span class="o">&lt;</span><span class="nb">String</span><span class="o">&gt;&gt;&gt;</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="n">cols</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>
<a href="#__codelineno-9-8" id="__codelineno-9-8" name="__codelineno-9-8"></a><span class="w"> </span><span class="n">diags1</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>
<a href="#__codelineno-9-9" id="__codelineno-9-9" name="__codelineno-9-9"></a><span class="w"> </span><span class="n">diags2</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>
<a href="#__codelineno-9-10" id="__codelineno-9-10" name="__codelineno-9-10"></a><span class="p">)</span><span class="w"> </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">// すべての行への配置が終わったら、解を記録する</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="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</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="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><span class="n">clone</span><span class="p">());</span>
<a href="#__codelineno-9-14" id="__codelineno-9-14" name="__codelineno-9-14"></a><span class="w"> </span><span class="k">return</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="p">}</span>
<a href="#__codelineno-9-16" id="__codelineno-9-16" name="__codelineno-9-16"></a><span class="w"> </span><span class="c1">// すべての列を走査する</span>
<a href="#__codelineno-9-17" id="__codelineno-9-17" name="__codelineno-9-17"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">col</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">n</span><span class="w"> </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">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-9-19" id="__codelineno-9-19" name="__codelineno-9-19"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</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="kd">let</span><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</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="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-9-22" id="__codelineno-9-22" name="__codelineno-9-22"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">cols</span><span class="p">[</span><span class="n">col</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">diags1</span><span class="p">[</span><span class="n">diag1</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">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">]</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-23" id="__codelineno-9-23" name="__codelineno-9-23"></a><span class="w"> </span><span class="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-9-24" id="__codelineno-9-24" name="__codelineno-9-24"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Q"</span><span class="p">.</span><span class="n">into</span><span class="p">();</span>
<a href="#__codelineno-9-25" id="__codelineno-9-25" name="__codelineno-9-25"></a><span class="w"> </span><span class="p">(</span><span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">],</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">],</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">])</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kc">true</span><span class="p">,</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w"> </span><span class="kc">true</span><span class="p">);</span>
<a href="#__codelineno-9-26" id="__codelineno-9-26" name="__codelineno-9-26"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-9-27" id="__codelineno-9-27" name="__codelineno-9-27"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-9-28" id="__codelineno-9-28" name="__codelineno-9-28"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-9-29" id="__codelineno-9-29" name="__codelineno-9-29"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"#"</span><span class="p">.</span><span class="n">into</span><span class="p">();</span>
<a href="#__codelineno-9-30" id="__codelineno-9-30" name="__codelineno-9-30"></a><span class="w"> </span><span class="p">(</span><span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">],</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">],</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">])</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kc">false</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w"> </span><span class="kc">false</span><span class="p">);</span>
<a href="#__codelineno-9-31" id="__codelineno-9-31" name="__codelineno-9-31"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-9-32" id="__codelineno-9-32" name="__codelineno-9-32"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-9-33" id="__codelineno-9-33" name="__codelineno-9-33"></a><span class="p">}</span>
<a href="#__codelineno-9-34" id="__codelineno-9-34" name="__codelineno-9-34"></a>
<a href="#__codelineno-9-35" id="__codelineno-9-35" name="__codelineno-9-35"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-9-36" id="__codelineno-9-36" name="__codelineno-9-36"></a><span class="k">fn</span><span class="w"> </span><span class="nf">n_queens</span><span class="p">(</span><span class="n">n</span><span class="p">:</span><span class="w"> </span><span class="kt">usize</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="nb">Vec</span><span class="o">&lt;</span><span class="nb">String</span><span class="o">&gt;&gt;&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-9-37" id="__codelineno-9-37" name="__codelineno-9-37"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-9-38" id="__codelineno-9-38" name="__codelineno-9-38"></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">state</span><span class="p">:</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="nb">String</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="fm">vec!</span><span class="p">[</span><span class="fm">vec!</span><span class="p">[</span><span class="s">"#"</span><span class="p">.</span><span class="n">to_string</span><span class="p">();</span><span class="w"> </span><span class="n">n</span><span class="p">];</span><span class="w"> </span><span class="n">n</span><span class="p">];</span>
<a href="#__codelineno-9-39" id="__codelineno-9-39" name="__codelineno-9-39"></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">cols</span><span class="w"> </span><span class="o">=</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">n</span><span class="p">];</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-9-40" id="__codelineno-9-40" name="__codelineno-9-40"></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">diags1</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-9-41" id="__codelineno-9-41" name="__codelineno-9-41"></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">diags2</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-9-42" id="__codelineno-9-42" name="__codelineno-9-42"></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="p">:</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="nb">Vec</span><span class="o">&lt;</span><span class="nb">String</span><span class="o">&gt;&gt;&gt;</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-9-43" id="__codelineno-9-43" name="__codelineno-9-43"></a>
<a href="#__codelineno-9-44" id="__codelineno-9-44" name="__codelineno-9-44"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span>
<a href="#__codelineno-9-45" id="__codelineno-9-45" name="__codelineno-9-45"></a><span class="w"> </span><span class="mi">0</span><span class="p">,</span>
<a href="#__codelineno-9-46" id="__codelineno-9-46" name="__codelineno-9-46"></a><span class="w"> </span><span class="n">n</span><span class="p">,</span>
<a href="#__codelineno-9-47" id="__codelineno-9-47" name="__codelineno-9-47"></a><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">state</span><span class="p">,</span>
<a href="#__codelineno-9-48" id="__codelineno-9-48" name="__codelineno-9-48"></a><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-9-49" id="__codelineno-9-49" name="__codelineno-9-49"></a><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">cols</span><span class="p">,</span>
<a href="#__codelineno-9-50" id="__codelineno-9-50" name="__codelineno-9-50"></a><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span>
<a href="#__codelineno-9-51" id="__codelineno-9-51" name="__codelineno-9-51"></a><span class="w"> </span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">diags2</span><span class="p">,</span>
<a href="#__codelineno-9-52" id="__codelineno-9-52" name="__codelineno-9-52"></a><span class="w"> </span><span class="p">);</span>
<a href="#__codelineno-9-53" id="__codelineno-9-53" name="__codelineno-9-53"></a>
<a href="#__codelineno-9-54" id="__codelineno-9-54" name="__codelineno-9-54"></a><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-9-55" id="__codelineno-9-55" name="__codelineno-9-55"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.c</span><pre><span></span><code><a href="#__codelineno-10-1" id="__codelineno-10-1" name="__codelineno-10-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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="n">row</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">MAX_SIZE</span><span class="p">][</span><span class="n">MAX_SIZE</span><span class="p">],</span><span class="w"> </span><span class="kt">char</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="kt">bool</span><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">MAX_SIZE</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="kt">bool</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">MAX_SIZE</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="kt">bool</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">MAX_SIZE</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="p">{</span>
<a href="#__codelineno-10-4" id="__codelineno-10-4" name="__codelineno-10-4"></a><span class="w"> </span><span class="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-10-5" id="__codelineno-10-5" name="__codelineno-10-5"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </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="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">char</span><span class="w"> </span><span class="o">**</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="k">sizeof</span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="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">n</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </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="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="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="k">sizeof</span><span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">n</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-10-9" id="__codelineno-10-9" name="__codelineno-10-9"></a><span class="w"> </span><span class="n">strcpy</span><span class="p">(</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="n">state</span><span class="p">[</span><span class="n">i</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="p">}</span>
<a href="#__codelineno-10-11" id="__codelineno-10-11" name="__codelineno-10-11"></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-10-12" id="__codelineno-10-12" name="__codelineno-10-12"></a><span class="w"> </span><span class="k">return</span><span class="p">;</span>
<a href="#__codelineno-10-13" id="__codelineno-10-13" name="__codelineno-10-13"></a><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="c1">// すべての列を走査する</span>
<a href="#__codelineno-10-15" id="__codelineno-10-15" name="__codelineno-10-15"></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">col</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">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">col</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-16" id="__codelineno-10-16" name="__codelineno-10-16"></a><span class="w"> </span><span class="c1">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-10-17" id="__codelineno-10-17" name="__codelineno-10-17"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</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-10-18" id="__codelineno-10-18" name="__codelineno-10-18"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</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="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-10-20" id="__codelineno-10-20" name="__codelineno-10-20"></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">cols</span><span class="p">[</span><span class="n">col</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">diags1</span><span class="p">[</span><span class="n">diag1</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">diags2</span><span class="p">[</span><span class="n">diag2</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-21" id="__codelineno-10-21" name="__codelineno-10-21"></a><span class="w"> </span><span class="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-10-22" id="__codelineno-10-22" name="__codelineno-10-22"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">'Q'</span><span class="p">;</span>
<a href="#__codelineno-10-23" id="__codelineno-10-23" name="__codelineno-10-23"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-10-24" id="__codelineno-10-24" name="__codelineno-10-24"></a><span class="w"> </span><span class="c1">// 次の行に配置する</span>
<a href="#__codelineno-10-25" id="__codelineno-10-25" name="__codelineno-10-25"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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><span class="w"> </span><span class="n">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-10-26" id="__codelineno-10-26" name="__codelineno-10-26"></a><span class="w"> </span><span class="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-10-27" id="__codelineno-10-27" name="__codelineno-10-27"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">row</span><span class="p">][</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">'#'</span><span class="p">;</span>
<a href="#__codelineno-10-28" id="__codelineno-10-28" name="__codelineno-10-28"></a><span class="w"> </span><span class="n">cols</span><span class="p">[</span><span class="n">col</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="n">diag1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="n">diag2</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-10-29" id="__codelineno-10-29" name="__codelineno-10-29"></a><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="p">}</span>
<a href="#__codelineno-10-31" id="__codelineno-10-31" name="__codelineno-10-31"></a><span class="p">}</span>
<a href="#__codelineno-10-32" id="__codelineno-10-32" name="__codelineno-10-32"></a>
<a href="#__codelineno-10-33" id="__codelineno-10-33" name="__codelineno-10-33"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-10-34" id="__codelineno-10-34" name="__codelineno-10-34"></a><span class="kt">char</span><span class="w"> </span><span class="o">***</span><span class="nf">nQueens</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</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-10-35" id="__codelineno-10-35" name="__codelineno-10-35"></a><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">MAX_SIZE</span><span class="p">][</span><span class="n">MAX_SIZE</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="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-10-37" id="__codelineno-10-37" name="__codelineno-10-37"></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">n</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-38" id="__codelineno-10-38" name="__codelineno-10-38"></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">j</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">j</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">j</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-10-39" id="__codelineno-10-39" name="__codelineno-10-39"></a><span class="w"> </span><span class="n">state</span><span class="p">[</span><span class="n">i</span><span class="p">][</span><span class="n">j</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">'#'</span><span class="p">;</span>
<a href="#__codelineno-10-40" id="__codelineno-10-40" name="__codelineno-10-40"></a><span class="w"> </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">state</span><span class="p">[</span><span class="n">i</span><span class="p">][</span><span class="n">n</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">'\0'</span><span class="p">;</span>
<a href="#__codelineno-10-42" id="__codelineno-10-42" name="__codelineno-10-42"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-10-43" id="__codelineno-10-43" name="__codelineno-10-43"></a><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">cols</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><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-10-44" id="__codelineno-10-44" name="__codelineno-10-44"></a><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">diags1</span><span class="p">[</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">MAX_SIZE</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="o">=</span><span class="w"> </span><span class="p">{</span><span class="nb">false</span><span class="p">};</span><span class="w"> </span><span class="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-10-45" id="__codelineno-10-45" name="__codelineno-10-45"></a><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">diags2</span><span class="p">[</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">MAX_SIZE</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="o">=</span><span class="w"> </span><span class="p">{</span><span class="nb">false</span><span class="p">};</span><span class="w"> </span><span class="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-10-46" id="__codelineno-10-46" name="__codelineno-10-46"></a>
<a href="#__codelineno-10-47" id="__codelineno-10-47" name="__codelineno-10-47"></a><span class="w"> </span><span class="kt">char</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">char</span><span class="w"> </span><span class="o">***</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="k">sizeof</span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="p">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">MAX_SIZE</span><span class="p">);</span>
<a href="#__codelineno-10-48" id="__codelineno-10-48" name="__codelineno-10-48"></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-10-49" id="__codelineno-10-49" name="__codelineno-10-49"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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><span class="w"> </span><span class="n">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">);</span>
<a href="#__codelineno-10-50" id="__codelineno-10-50" name="__codelineno-10-50"></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-10-51" id="__codelineno-10-51" name="__codelineno-10-51"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.kt</span><pre><span></span><code><a href="#__codelineno-11-1" id="__codelineno-11-1" name="__codelineno-11-1"></a><span class="cm">/* バックトラッキング:n クイーン */</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">row</span><span class="p">:</span><span class="w"> </span><span class="kt">Int</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">n</span><span class="p">:</span><span class="w"> </span><span class="kt">Int</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">state</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">String</span><span class="o">&gt;&gt;</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="n">MutableList</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&gt;?&gt;</span><span class="p">,</span>
<a href="#__codelineno-11-7" id="__codelineno-11-7" name="__codelineno-11-7"></a><span class="w"> </span><span class="n">cols</span><span class="p">:</span><span class="w"> </span><span class="n">BooleanArray</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="n">diags1</span><span class="p">:</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">,</span>
<a href="#__codelineno-11-9" id="__codelineno-11-9" name="__codelineno-11-9"></a><span class="w"> </span><span class="n">diags2</span><span class="p">:</span><span class="w"> </span><span class="n">BooleanArray</span>
<a href="#__codelineno-11-10" id="__codelineno-11-10" name="__codelineno-11-10"></a><span class="p">)</span><span class="w"> </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="c1">// すべての行への配置が終わったら、解を記録する</span>
<a href="#__codelineno-11-12" id="__codelineno-11-12" name="__codelineno-11-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><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="kd">val</span><span class="w"> </span><span class="nv">copyState</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">String</span><span class="o">&gt;&gt;</span><span class="p">()</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">sRow</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">state</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="n">copyState</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">sRow</span><span class="p">.</span><span class="na">toMutableList</span><span class="p">())</span>
<a href="#__codelineno-11-16" id="__codelineno-11-16" name="__codelineno-11-16"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-17" id="__codelineno-11-17" name="__codelineno-11-17"></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">copyState</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="k">return</span>
<a href="#__codelineno-11-19" id="__codelineno-11-19" name="__codelineno-11-19"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-20" id="__codelineno-11-20" name="__codelineno-11-20"></a><span class="w"> </span><span class="c1">// すべての列を走査する</span>
<a href="#__codelineno-11-21" id="__codelineno-11-21" name="__codelineno-11-21"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">col</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="m">0.</span><span class="p">.</span><span class="o">&lt;</span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-22" id="__codelineno-11-22" name="__codelineno-11-22"></a><span class="w"> </span><span class="c1">// このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-11-23" id="__codelineno-11-23" name="__codelineno-11-23"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span>
<a href="#__codelineno-11-24" id="__codelineno-11-24" name="__codelineno-11-24"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</span>
<a href="#__codelineno-11-25" id="__codelineno-11-25" name="__codelineno-11-25"></a><span class="w"> </span><span class="c1">// 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-11-26" id="__codelineno-11-26" name="__codelineno-11-26"></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">cols</span><span class="o">[</span><span class="n">col</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">diags1</span><span class="o">[</span><span class="n">diag1</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">diags2</span><span class="o">[</span><span class="n">diag2</span><span class="o">]</span><span class="p">)</span><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="c1">// 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-11-28" id="__codelineno-11-28" name="__codelineno-11-28"></a><span class="w"> </span><span class="n">state</span><span class="o">[</span><span class="n">row</span><span class="o">][</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Q"</span>
<a href="#__codelineno-11-29" id="__codelineno-11-29" name="__codelineno-11-29"></a><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</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-11-30" id="__codelineno-11-30" name="__codelineno-11-30"></a><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</span><span class="o">]</span>
<a href="#__codelineno-11-31" id="__codelineno-11-31" name="__codelineno-11-31"></a><span class="w"> </span><span class="n">cols</span><span class="o">[</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span>
<a href="#__codelineno-11-32" id="__codelineno-11-32" name="__codelineno-11-32"></a><span class="w"> </span><span class="c1">// 次の行に配置する</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">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="m">1</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</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="c1">// 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-11-35" id="__codelineno-11-35" name="__codelineno-11-35"></a><span class="w"> </span><span class="n">state</span><span class="o">[</span><span class="n">row</span><span class="o">][</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"#"</span>
<a href="#__codelineno-11-36" id="__codelineno-11-36" name="__codelineno-11-36"></a><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</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-11-37" id="__codelineno-11-37" name="__codelineno-11-37"></a><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</span><span class="o">]</span>
<a href="#__codelineno-11-38" id="__codelineno-11-38" name="__codelineno-11-38"></a><span class="w"> </span><span class="n">cols</span><span class="o">[</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span>
<a href="#__codelineno-11-39" id="__codelineno-11-39" name="__codelineno-11-39"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-40" id="__codelineno-11-40" name="__codelineno-11-40"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-41" id="__codelineno-11-41" name="__codelineno-11-41"></a><span class="p">}</span>
<a href="#__codelineno-11-42" id="__codelineno-11-42" name="__codelineno-11-42"></a>
<a href="#__codelineno-11-43" id="__codelineno-11-43" name="__codelineno-11-43"></a><span class="cm">/* n クイーン問題を解く */</span>
<a href="#__codelineno-11-44" id="__codelineno-11-44" name="__codelineno-11-44"></a><span class="kd">fun</span><span class="w"> </span><span class="nf">nQueens</span><span class="p">(</span><span class="n">n</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">MutableList</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="n">MutableList</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&gt;?&gt;</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-45" id="__codelineno-11-45" name="__codelineno-11-45"></a><span class="w"> </span><span class="c1">// n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-11-46" id="__codelineno-11-46" name="__codelineno-11-46"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">state</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">String</span><span class="o">&gt;&gt;</span><span class="p">()</span>
<a href="#__codelineno-11-47" id="__codelineno-11-47" name="__codelineno-11-47"></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="m">0.</span><span class="p">.</span><span class="o">&lt;</span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-48" id="__codelineno-11-48" name="__codelineno-11-48"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">row</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="kt">String</span><span class="o">&gt;</span><span class="p">()</span>
<a href="#__codelineno-11-49" id="__codelineno-11-49" name="__codelineno-11-49"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">j</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="m">0.</span><span class="p">.</span><span class="o">&lt;</span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a href="#__codelineno-11-50" id="__codelineno-11-50" name="__codelineno-11-50"></a><span class="w"> </span><span class="n">row</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="s">"#"</span><span class="p">)</span>
<a href="#__codelineno-11-51" id="__codelineno-11-51" name="__codelineno-11-51"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-52" id="__codelineno-11-52" name="__codelineno-11-52"></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">row</span><span class="p">)</span>
<a href="#__codelineno-11-53" id="__codelineno-11-53" name="__codelineno-11-53"></a><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-11-54" id="__codelineno-11-54" name="__codelineno-11-54"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">cols</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">(</span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="c1">// 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-11-55" id="__codelineno-11-55" name="__codelineno-11-55"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">diags1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">(</span><span class="m">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">)</span><span class="w"> </span><span class="c1">// 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-11-56" id="__codelineno-11-56" name="__codelineno-11-56"></a><span class="w"> </span><span class="kd">val</span><span class="w"> </span><span class="nv">diags2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BooleanArray</span><span class="p">(</span><span class="m">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">)</span><span class="w"> </span><span class="c1">// 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-11-57" id="__codelineno-11-57" name="__codelineno-11-57"></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="n">MutableList</span><span class="o">&lt;</span><span class="kt">String</span><span class="o">&gt;&gt;?&gt;</span><span class="p">()</span>
<a href="#__codelineno-11-58" id="__codelineno-11-58" name="__codelineno-11-58"></a>
<a href="#__codelineno-11-59" id="__codelineno-11-59" name="__codelineno-11-59"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="m">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-11-60" id="__codelineno-11-60" name="__codelineno-11-60"></a>
<a href="#__codelineno-11-61" id="__codelineno-11-61" name="__codelineno-11-61"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-11-62" id="__codelineno-11-62" name="__codelineno-11-62"></a><span class="p">}</span>
</code></pre></div>
</div>
<div class="tabbed-block">
<div class="highlight"><span class="filename">n_queens.rb</span><pre><span></span><code><a href="#__codelineno-12-1" id="__codelineno-12-1" name="__codelineno-12-1"></a><span class="c1">### バックトラッキング:n クイーン ###</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">row</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</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"># すべての行への配置が終わったら、解を記録する</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">row</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">n</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">map</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">|</span><span class="n">row</span><span class="o">|</span><span class="w"> </span><span class="n">row</span><span class="o">.</span><span class="n">dup</span><span class="w"> </span><span class="p">}</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"># すべての列を走査する</span>
<a href="#__codelineno-12-10" id="__codelineno-12-10" name="__codelineno-12-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">col</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">n</span>
<a href="#__codelineno-12-11" id="__codelineno-12-11" name="__codelineno-12-11"></a><span class="w"> </span><span class="c1"># このマスに対応する主対角線と副対角線を求める</span>
<a href="#__codelineno-12-12" id="__codelineno-12-12" name="__codelineno-12-12"></a><span class="w"> </span><span class="n">diag1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span>
<a href="#__codelineno-12-13" id="__codelineno-12-13" name="__codelineno-12-13"></a><span class="w"> </span><span class="n">diag2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">col</span>
<a href="#__codelineno-12-14" id="__codelineno-12-14" name="__codelineno-12-14"></a><span class="w"> </span><span class="c1"># 枝刈り:このマスと同じ列、主対角線、副対角線にクイーンがあってはならない</span>
<a href="#__codelineno-12-15" id="__codelineno-12-15" name="__codelineno-12-15"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="o">!</span><span class="n">cols</span><span class="o">[</span><span class="n">col</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">diags1</span><span class="o">[</span><span class="n">diag1</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">diags2</span><span class="o">[</span><span class="n">diag2</span><span class="o">]</span>
<a href="#__codelineno-12-16" id="__codelineno-12-16" name="__codelineno-12-16"></a><span class="w"> </span><span class="c1"># 試行:このマスにクイーンを配置する</span>
<a href="#__codelineno-12-17" id="__codelineno-12-17" name="__codelineno-12-17"></a><span class="w"> </span><span class="n">state</span><span class="o">[</span><span class="n">row</span><span class="o">][</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">"Q"</span>
<a href="#__codelineno-12-18" id="__codelineno-12-18" name="__codelineno-12-18"></a><span class="w"> </span><span class="n">cols</span><span class="o">[</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</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-12-19" id="__codelineno-12-19" name="__codelineno-12-19"></a><span class="w"> </span><span class="c1"># 次の行に配置する</span>
<a href="#__codelineno-12-20" id="__codelineno-12-20" name="__codelineno-12-20"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="n">row</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">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-12-21" id="__codelineno-12-21" name="__codelineno-12-21"></a><span class="w"> </span><span class="c1"># 復元:このマスを空きマスに戻す</span>
<a href="#__codelineno-12-22" id="__codelineno-12-22" name="__codelineno-12-22"></a><span class="w"> </span><span class="n">state</span><span class="o">[</span><span class="n">row</span><span class="o">][</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">"#"</span>
<a href="#__codelineno-12-23" id="__codelineno-12-23" name="__codelineno-12-23"></a><span class="w"> </span><span class="n">cols</span><span class="o">[</span><span class="n">col</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags1</span><span class="o">[</span><span class="n">diag1</span><span class="o">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">diags2</span><span class="o">[</span><span class="n">diag2</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-12-24" id="__codelineno-12-24" name="__codelineno-12-24"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-12-25" id="__codelineno-12-25" name="__codelineno-12-25"></a><span class="w"> </span><span class="k">end</span>
<a href="#__codelineno-12-26" id="__codelineno-12-26" name="__codelineno-12-26"></a><span class="k">end</span>
<a href="#__codelineno-12-27" id="__codelineno-12-27" name="__codelineno-12-27"></a>
<a href="#__codelineno-12-28" id="__codelineno-12-28" name="__codelineno-12-28"></a><span class="c1">### n クイーン問題を解く ###</span>
<a href="#__codelineno-12-29" id="__codelineno-12-29" name="__codelineno-12-29"></a><span class="k">def</span><span class="w"> </span><span class="nf">n_queens</span><span class="p">(</span><span class="n">n</span><span class="p">)</span>
<a href="#__codelineno-12-30" id="__codelineno-12-30" name="__codelineno-12-30"></a><span class="w"> </span><span class="c1"># n*n の盤面を初期化する。'Q' はクイーン、'#' は空きマスを表す</span>
<a href="#__codelineno-12-31" id="__codelineno-12-31" name="__codelineno-12-31"></a><span class="w"> </span><span class="n">state</span><span class="w"> </span><span class="o">=</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">n</span><span class="p">)</span><span class="w"> </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">n</span><span class="p">,</span><span class="w"> </span><span class="s2">"#"</span><span class="p">)</span><span class="w"> </span><span class="p">}</span>
<a href="#__codelineno-12-32" id="__codelineno-12-32" name="__codelineno-12-32"></a><span class="w"> </span><span class="n">cols</span><span class="w"> </span><span class="o">=</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">n</span><span class="p">,</span><span class="w"> </span><span class="kp">false</span><span class="p">)</span><span class="w"> </span><span class="c1"># 列にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-12-33" id="__codelineno-12-33" name="__codelineno-12-33"></a><span class="w"> </span><span class="n">diags1</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="kp">false</span><span class="p">)</span><span class="w"> </span><span class="c1"># 主対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-12-34" id="__codelineno-12-34" name="__codelineno-12-34"></a><span class="w"> </span><span class="n">diags2</span><span class="w"> </span><span class="o">=</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="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">n</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="kp">false</span><span class="p">)</span><span class="w"> </span><span class="c1"># 副対角線にクイーンがあるかどうかを記録する</span>
<a href="#__codelineno-12-35" id="__codelineno-12-35" name="__codelineno-12-35"></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-12-36" id="__codelineno-12-36" name="__codelineno-12-36"></a><span class="w"> </span><span class="n">backtrack</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">state</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">cols</span><span class="p">,</span><span class="w"> </span><span class="n">diags1</span><span class="p">,</span><span class="w"> </span><span class="n">diags2</span><span class="p">)</span>
<a href="#__codelineno-12-37" id="__codelineno-12-37" name="__codelineno-12-37"></a>
<a href="#__codelineno-12-38" id="__codelineno-12-38" name="__codelineno-12-38"></a><span class="w"> </span><span class="n">res</span>
<a href="#__codelineno-12-39" id="__codelineno-12-39" name="__codelineno-12-39"></a><span class="k">end</span>
</code></pre></div>
</div>
</div>
</div>
<details class="pythontutor">
<summary>実行の可視化</summary>
<p><div style="height: 549px; width: 100%;"><iframe class="pythontutor-iframe" 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title="実行の可視化"> </iframe></div>
<div style="margin-top: 5px;"><a 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rel="noopener noreferrer" target="_blank">全画面で表示 &gt;</a></div></p>
</details>
<p>行ごとの配置を <span class="arithmatex">\(n\)</span> 回行います。列の制約を考慮すると、先頭行から最後の行までの選択肢は <span class="arithmatex">\(n\)</span>、<span class="arithmatex">\(n-1\)</span>、<span class="arithmatex">\(\dots\)</span>、<span class="arithmatex">\(2\)</span>、<span class="arithmatex">\(1\)</span> 個なので、<span class="arithmatex">\(O(n!)\)</span> 時間かかります。解を記録するときは行列 <code>state</code> をコピーして <code>res</code> に追加し、コピーには <span class="arithmatex">\(O(n^2)\)</span> 時間かかります。したがって、<strong>全体の時間計算量は <span class="arithmatex">\(O(n! \cdot n^2)\)</span> です</strong>。実際には、対角線の制約による枝刈りでも探索空間が大きく減るため、この計算量から想定されるより効率よく探索できることが多くなります。</p>
<p>配列 <code>state</code> は <span class="arithmatex">\(O(n^2)\)</span>、配列 <code>cols</code>、<code>diags1</code>、<code>diags2</code> はそれぞれ <span class="arithmatex">\(O(n)\)</span> の空間を使います。最大再帰深度は <span class="arithmatex">\(n\)</span> なので、スタックフレームに <span class="arithmatex">\(O(n)\)</span> の空間を使います。したがって、<strong>空間計算量は <span class="arithmatex">\(O(n^2)\)</span> です</strong>。</p>
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