deploy

chapter_backtracking/backtracking_algorithm/index.html

@@ -1572,6 +1572,8 @@
         
           
         
+          
+        
       
       
         <label class="md-nav__link" for="__nav_14" id="__nav_14_label" tabindex="0">
@@ -1683,6 +1685,20 @@
 
             
           
+            
+              
+  
+  
+  
+    <li class="md-nav__item">
+      <a href="../n_queens_problem/" class="md-nav__link">
+        13.3. &nbsp; n 皇后问题（New）
+      </a>
+    </li>
+  
+
+            
+          
         </ul>
       </nav>
     </li>
@@ -1974,7 +1990,18 @@
 </code></pre></div>
 </div>
 <div class="tabbed-block">
-<div class="highlight"><span class="filename">preorder_traversal_i_compact.swift</span><pre><span></span><code><a id="__codelineno-8-1" name="__codelineno-8-1" href="#__codelineno-8-1"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">preOrder</span><span class="p">}</span>
+<div class="highlight"><span class="filename">preorder_traversal_i_compact.swift</span><pre><span></span><code><a id="__codelineno-8-1" name="__codelineno-8-1" href="#__codelineno-8-1"></a><span class="cm">/* 前序遍历：例题一 */</span>
+<a id="__codelineno-8-2" name="__codelineno-8-2" href="#__codelineno-8-2"></a><span class="kd">func</span> <span class="nf">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">TreeNode</span><span class="p">?)</span> <span class="p">{</span>
+<a id="__codelineno-8-3" name="__codelineno-8-3" href="#__codelineno-8-3"></a>    <span class="k">guard</span> <span class="kd">let</span> <span class="nv">root</span> <span class="p">=</span> <span class="n">root</span> <span class="k">else</span> <span class="p">{</span>
+<a id="__codelineno-8-4" name="__codelineno-8-4" href="#__codelineno-8-4"></a>        <span class="k">return</span>
+<a id="__codelineno-8-5" name="__codelineno-8-5" href="#__codelineno-8-5"></a>    <span class="p">}</span>
+<a id="__codelineno-8-6" name="__codelineno-8-6" href="#__codelineno-8-6"></a>    <span class="k">if</span> <span class="n">root</span><span class="p">.</span><span class="n">val</span> <span class="p">==</span> <span class="mi">7</span> <span class="p">{</span>
+<a id="__codelineno-8-7" name="__codelineno-8-7" href="#__codelineno-8-7"></a>        <span class="c1">// 记录解</span>
+<a id="__codelineno-8-8" name="__codelineno-8-8" href="#__codelineno-8-8"></a>        <span class="n">res</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
+<a id="__codelineno-8-9" name="__codelineno-8-9" href="#__codelineno-8-9"></a>    <span class="p">}</span>
+<a id="__codelineno-8-10" name="__codelineno-8-10" href="#__codelineno-8-10"></a>    <span class="n">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">root</span><span class="p">.</span><span class="kr">left</span><span class="p">)</span>
+<a id="__codelineno-8-11" name="__codelineno-8-11" href="#__codelineno-8-11"></a>    <span class="n">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">root</span><span class="p">.</span><span class="kr">right</span><span class="p">)</span>
+<a id="__codelineno-8-12" name="__codelineno-8-12" href="#__codelineno-8-12"></a><span class="p">}</span>
 </code></pre></div>
 </div>
 <div class="tabbed-block">
@@ -2086,7 +2113,22 @@
 </code></pre></div>
 </div>
 <div class="tabbed-block">
-<div class="highlight"><span class="filename">preorder_traversal_ii_compact.swift</span><pre><span></span><code><a id="__codelineno-18-1" name="__codelineno-18-1" href="#__codelineno-18-1"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">preOrder</span><span class="p">}</span>
+<div class="highlight"><span class="filename">preorder_traversal_ii_compact.swift</span><pre><span></span><code><a id="__codelineno-18-1" name="__codelineno-18-1" href="#__codelineno-18-1"></a><span class="cm">/* 前序遍历：例题二 */</span>
+<a id="__codelineno-18-2" name="__codelineno-18-2" href="#__codelineno-18-2"></a><span class="kd">func</span> <span class="nf">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">TreeNode</span><span class="p">?)</span> <span class="p">{</span>
+<a id="__codelineno-18-3" name="__codelineno-18-3" href="#__codelineno-18-3"></a>    <span class="k">guard</span> <span class="kd">let</span> <span class="nv">root</span> <span class="p">=</span> <span class="n">root</span> <span class="k">else</span> <span class="p">{</span>
+<a id="__codelineno-18-4" name="__codelineno-18-4" href="#__codelineno-18-4"></a>        <span class="k">return</span>
+<a id="__codelineno-18-5" name="__codelineno-18-5" href="#__codelineno-18-5"></a>    <span class="p">}</span>
+<a id="__codelineno-18-6" name="__codelineno-18-6" href="#__codelineno-18-6"></a>    <span class="c1">// 尝试</span>
+<a id="__codelineno-18-7" name="__codelineno-18-7" href="#__codelineno-18-7"></a>    <span class="n">path</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
+<a id="__codelineno-18-8" name="__codelineno-18-8" href="#__codelineno-18-8"></a>    <span class="k">if</span> <span class="n">root</span><span class="p">.</span><span class="n">val</span> <span class="p">==</span> <span class="mi">7</span> <span class="p">{</span>
+<a id="__codelineno-18-9" name="__codelineno-18-9" href="#__codelineno-18-9"></a>        <span class="c1">// 记录解</span>
+<a id="__codelineno-18-10" name="__codelineno-18-10" href="#__codelineno-18-10"></a>        <span class="n">res</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
+<a id="__codelineno-18-11" name="__codelineno-18-11" href="#__codelineno-18-11"></a>    <span class="p">}</span>
+<a id="__codelineno-18-12" name="__codelineno-18-12" href="#__codelineno-18-12"></a>    <span class="n">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">root</span><span class="p">.</span><span class="kr">left</span><span class="p">)</span>
+<a id="__codelineno-18-13" name="__codelineno-18-13" href="#__codelineno-18-13"></a>    <span class="n">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">root</span><span class="p">.</span><span class="kr">right</span><span class="p">)</span>
+<a id="__codelineno-18-14" name="__codelineno-18-14" href="#__codelineno-18-14"></a>    <span class="c1">// 回退</span>
+<a id="__codelineno-18-15" name="__codelineno-18-15" href="#__codelineno-18-15"></a>    <span class="n">path</span><span class="p">.</span><span class="bp">removeLast</span><span class="p">()</span>
+<a id="__codelineno-18-16" name="__codelineno-18-16" href="#__codelineno-18-16"></a><span class="p">}</span>
 </code></pre></div>
 </div>
 <div class="tabbed-block">
@@ -2235,7 +2277,23 @@
 </code></pre></div>
 </div>
 <div class="tabbed-block">
-<div class="highlight"><span class="filename">preorder_traversal_iii_compact.swift</span><pre><span></span><code><a id="__codelineno-28-1" name="__codelineno-28-1" href="#__codelineno-28-1"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">preOrder</span><span class="p">}</span>
+<div class="highlight"><span class="filename">preorder_traversal_iii_compact.swift</span><pre><span></span><code><a id="__codelineno-28-1" name="__codelineno-28-1" href="#__codelineno-28-1"></a><span class="cm">/* 前序遍历：例题三 */</span>
+<a id="__codelineno-28-2" name="__codelineno-28-2" href="#__codelineno-28-2"></a><span class="kd">func</span> <span class="nf">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">TreeNode</span><span class="p">?)</span> <span class="p">{</span>
+<a id="__codelineno-28-3" name="__codelineno-28-3" href="#__codelineno-28-3"></a>    <span class="c1">// 剪枝</span>
+<a id="__codelineno-28-4" name="__codelineno-28-4" href="#__codelineno-28-4"></a>    <span class="k">guard</span> <span class="kd">let</span> <span class="nv">root</span> <span class="p">=</span> <span class="n">root</span><span class="p">,</span> <span class="n">root</span><span class="p">.</span><span class="n">val</span> <span class="o">!=</span> <span class="mi">3</span> <span class="k">else</span> <span class="p">{</span>
+<a id="__codelineno-28-5" name="__codelineno-28-5" href="#__codelineno-28-5"></a>        <span class="k">return</span>
+<a id="__codelineno-28-6" name="__codelineno-28-6" href="#__codelineno-28-6"></a>    <span class="p">}</span>
+<a id="__codelineno-28-7" name="__codelineno-28-7" href="#__codelineno-28-7"></a>    <span class="c1">// 尝试</span>
+<a id="__codelineno-28-8" name="__codelineno-28-8" href="#__codelineno-28-8"></a>    <span class="n">path</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
+<a id="__codelineno-28-9" name="__codelineno-28-9" href="#__codelineno-28-9"></a>    <span class="k">if</span> <span class="n">root</span><span class="p">.</span><span class="n">val</span> <span class="p">==</span> <span class="mi">7</span> <span class="p">{</span>
+<a id="__codelineno-28-10" name="__codelineno-28-10" href="#__codelineno-28-10"></a>        <span class="c1">// 记录解</span>
+<a id="__codelineno-28-11" name="__codelineno-28-11" href="#__codelineno-28-11"></a>        <span class="n">res</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
+<a id="__codelineno-28-12" name="__codelineno-28-12" href="#__codelineno-28-12"></a>    <span class="p">}</span>
+<a id="__codelineno-28-13" name="__codelineno-28-13" href="#__codelineno-28-13"></a>    <span class="n">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">root</span><span class="p">.</span><span class="kr">left</span><span class="p">)</span>
+<a id="__codelineno-28-14" name="__codelineno-28-14" href="#__codelineno-28-14"></a>    <span class="n">preOrder</span><span class="p">(</span><span class="n">root</span><span class="p">:</span> <span class="n">root</span><span class="p">.</span><span class="kr">right</span><span class="p">)</span>
+<a id="__codelineno-28-15" name="__codelineno-28-15" href="#__codelineno-28-15"></a>    <span class="c1">// 回退</span>
+<a id="__codelineno-28-16" name="__codelineno-28-16" href="#__codelineno-28-16"></a>    <span class="n">path</span><span class="p">.</span><span class="bp">removeLast</span><span class="p">()</span>
+<a id="__codelineno-28-17" name="__codelineno-28-17" href="#__codelineno-28-17"></a><span class="p">}</span>
 </code></pre></div>
 </div>
 <div class="tabbed-block">
@@ -2563,17 +2621,51 @@
 </code></pre></div>
 </div>
 <div class="tabbed-block">
-<div class="highlight"><span class="filename">preorder_traversal_iii_template.swift</span><pre><span></span><code><a id="__codelineno-39-1" name="__codelineno-39-1" href="#__codelineno-39-1"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">isSolution</span><span class="p">}</span>
-<a id="__codelineno-39-2" name="__codelineno-39-2" href="#__codelineno-39-2"></a>
-<a id="__codelineno-39-3" name="__codelineno-39-3" href="#__codelineno-39-3"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">recordSolution</span><span class="p">}</span>
-<a id="__codelineno-39-4" name="__codelineno-39-4" href="#__codelineno-39-4"></a>
-<a id="__codelineno-39-5" name="__codelineno-39-5" href="#__codelineno-39-5"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">isValid</span><span class="p">}</span>
-<a id="__codelineno-39-6" name="__codelineno-39-6" href="#__codelineno-39-6"></a>
-<a id="__codelineno-39-7" name="__codelineno-39-7" href="#__codelineno-39-7"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">makeChoice</span><span class="p">}</span>
-<a id="__codelineno-39-8" name="__codelineno-39-8" href="#__codelineno-39-8"></a>
-<a id="__codelineno-39-9" name="__codelineno-39-9" href="#__codelineno-39-9"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">undoChoice</span><span class="p">}</span>
+<div class="highlight"><span class="filename">preorder_traversal_iii_template.swift</span><pre><span></span><code><a id="__codelineno-39-1" name="__codelineno-39-1" href="#__codelineno-39-1"></a><span class="cm">/* 判断当前状态是否为解 */</span>
+<a id="__codelineno-39-2" name="__codelineno-39-2" href="#__codelineno-39-2"></a><span class="kd">func</span> <span class="nf">isSolution</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">])</span> <span class="p">-&gt;</span> <span class="nb">Bool</span> <span class="p">{</span>
+<a id="__codelineno-39-3" name="__codelineno-39-3" href="#__codelineno-39-3"></a>    <span class="o">!</span><span class="n">state</span><span class="p">.</span><span class="bp">isEmpty</span> <span class="o">&amp;&amp;</span> <span class="n">state</span><span class="p">.</span><span class="bp">last</span><span class="p">!.</span><span class="n">val</span> <span class="p">==</span> <span class="mi">7</span>
+<a id="__codelineno-39-4" name="__codelineno-39-4" href="#__codelineno-39-4"></a><span class="p">}</span>
+<a id="__codelineno-39-5" name="__codelineno-39-5" href="#__codelineno-39-5"></a>
+<a id="__codelineno-39-6" name="__codelineno-39-6" href="#__codelineno-39-6"></a><span class="cm">/* 记录解 */</span>
+<a id="__codelineno-39-7" name="__codelineno-39-7" href="#__codelineno-39-7"></a><span class="kd">func</span> <span class="nf">recordSolution</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">],</span> <span class="n">res</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[[</span><span class="n">TreeNode</span><span class="p">]])</span> <span class="p">{</span>
+<a id="__codelineno-39-8" name="__codelineno-39-8" href="#__codelineno-39-8"></a>    <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 id="__codelineno-39-9" name="__codelineno-39-9" href="#__codelineno-39-9"></a><span class="p">}</span>
 <a id="__codelineno-39-10" name="__codelineno-39-10" href="#__codelineno-39-10"></a>
-<a id="__codelineno-39-11" name="__codelineno-39-11" href="#__codelineno-39-11"></a><span class="p">[</span><span class="kd">class</span><span class="p">]{}</span><span class="o">-</span><span class="p">[</span><span class="kd">func</span><span class="p">]{</span><span class="n">backtrack</span><span class="p">}</span>
+<a id="__codelineno-39-11" name="__codelineno-39-11" href="#__codelineno-39-11"></a><span class="cm">/* 判断在当前状态下，该选择是否合法 */</span>
+<a id="__codelineno-39-12" name="__codelineno-39-12" href="#__codelineno-39-12"></a><span class="kd">func</span> <span class="nf">isValid</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">],</span> <span class="n">choice</span><span class="p">:</span> <span class="n">TreeNode</span><span class="p">?)</span> <span class="p">-&gt;</span> <span class="nb">Bool</span> <span class="p">{</span>
+<a id="__codelineno-39-13" name="__codelineno-39-13" href="#__codelineno-39-13"></a>    <span class="n">choice</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="o">&amp;&amp;</span> <span class="n">choice</span><span class="p">!.</span><span class="n">val</span> <span class="o">!=</span> <span class="mi">3</span>
+<a id="__codelineno-39-14" name="__codelineno-39-14" href="#__codelineno-39-14"></a><span class="p">}</span>
+<a id="__codelineno-39-15" name="__codelineno-39-15" href="#__codelineno-39-15"></a>
+<a id="__codelineno-39-16" name="__codelineno-39-16" href="#__codelineno-39-16"></a><span class="cm">/* 更新状态 */</span>
+<a id="__codelineno-39-17" name="__codelineno-39-17" href="#__codelineno-39-17"></a><span class="kd">func</span> <span class="nf">makeChoice</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">],</span> <span class="n">choice</span><span class="p">:</span> <span class="n">TreeNode</span><span class="p">)</span> <span class="p">{</span>
+<a id="__codelineno-39-18" name="__codelineno-39-18" href="#__codelineno-39-18"></a>    <span class="n">state</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">choice</span><span class="p">)</span>
+<a id="__codelineno-39-19" name="__codelineno-39-19" href="#__codelineno-39-19"></a><span class="p">}</span>
+<a id="__codelineno-39-20" name="__codelineno-39-20" href="#__codelineno-39-20"></a>
+<a id="__codelineno-39-21" name="__codelineno-39-21" href="#__codelineno-39-21"></a><span class="cm">/* 恢复状态 */</span>
+<a id="__codelineno-39-22" name="__codelineno-39-22" href="#__codelineno-39-22"></a><span class="kd">func</span> <span class="nf">undoChoice</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">],</span> <span class="n">choice</span><span class="p">:</span> <span class="n">TreeNode</span><span class="p">)</span> <span class="p">{</span>
+<a id="__codelineno-39-23" name="__codelineno-39-23" href="#__codelineno-39-23"></a>    <span class="n">state</span><span class="p">.</span><span class="bp">removeLast</span><span class="p">()</span>
+<a id="__codelineno-39-24" name="__codelineno-39-24" href="#__codelineno-39-24"></a><span class="p">}</span>
+<a id="__codelineno-39-25" name="__codelineno-39-25" href="#__codelineno-39-25"></a>
+<a id="__codelineno-39-26" name="__codelineno-39-26" href="#__codelineno-39-26"></a><span class="cm">/* 回溯算法：例题三 */</span>
+<a id="__codelineno-39-27" name="__codelineno-39-27" href="#__codelineno-39-27"></a><span class="kd">func</span> <span class="nf">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">],</span> <span class="n">choices</span><span class="p">:</span> <span class="p">[</span><span class="n">TreeNode</span><span class="p">],</span> <span class="n">res</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[[</span><span class="n">TreeNode</span><span class="p">]])</span> <span class="p">{</span>
+<a id="__codelineno-39-28" name="__codelineno-39-28" href="#__codelineno-39-28"></a>    <span class="c1">// 检查是否为解</span>
+<a id="__codelineno-39-29" name="__codelineno-39-29" href="#__codelineno-39-29"></a>    <span class="k">if</span> <span class="n">isSolution</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="n">state</span><span class="p">)</span> <span class="p">{</span>
+<a id="__codelineno-39-30" name="__codelineno-39-30" href="#__codelineno-39-30"></a>        <span class="n">recordSolution</span><span class="p">(</span><span class="n">state</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="p">&amp;</span><span class="n">res</span><span class="p">)</span>
+<a id="__codelineno-39-31" name="__codelineno-39-31" href="#__codelineno-39-31"></a>        <span class="k">return</span>
+<a id="__codelineno-39-32" name="__codelineno-39-32" href="#__codelineno-39-32"></a>    <span class="p">}</span>
+<a id="__codelineno-39-33" name="__codelineno-39-33" href="#__codelineno-39-33"></a>    <span class="c1">// 遍历所有选择</span>
+<a id="__codelineno-39-34" name="__codelineno-39-34" href="#__codelineno-39-34"></a>    <span class="k">for</span> <span class="n">choice</span> <span class="k">in</span> <span class="n">choices</span> <span class="p">{</span>
+<a id="__codelineno-39-35" name="__codelineno-39-35" href="#__codelineno-39-35"></a>        <span class="c1">// 剪枝：检查选择是否合法</span>
+<a id="__codelineno-39-36" name="__codelineno-39-36" href="#__codelineno-39-36"></a>        <span class="k">if</span> <span class="n">isValid</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="n">state</span><span class="p">,</span> <span class="n">choice</span><span class="p">:</span> <span class="n">choice</span><span class="p">)</span> <span class="p">{</span>
+<a id="__codelineno-39-37" name="__codelineno-39-37" href="#__codelineno-39-37"></a>            <span class="c1">// 尝试：做出选择，更新状态</span>
+<a id="__codelineno-39-38" name="__codelineno-39-38" href="#__codelineno-39-38"></a>            <span class="n">makeChoice</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">state</span><span class="p">,</span> <span class="n">choice</span><span class="p">:</span> <span class="n">choice</span><span class="p">)</span>
+<a id="__codelineno-39-39" name="__codelineno-39-39" href="#__codelineno-39-39"></a>            <span class="c1">// 进行下一轮选择</span>
+<a id="__codelineno-39-40" name="__codelineno-39-40" href="#__codelineno-39-40"></a>            <span class="n">backtrack</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">state</span><span class="p">,</span> <span class="n">choices</span><span class="p">:</span> <span class="p">[</span><span class="n">choice</span><span class="p">.</span><span class="kr">left</span><span class="p">,</span> <span class="n">choice</span><span class="p">.</span><span class="kr">right</span><span class="p">].</span><span class="n">compactMap</span> <span class="p">{</span> <span class="nv">$0</span> <span class="p">},</span> <span class="n">res</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">res</span><span class="p">)</span>
+<a id="__codelineno-39-41" name="__codelineno-39-41" href="#__codelineno-39-41"></a>            <span class="c1">// 回退：撤销选择，恢复到之前的状态</span>
+<a id="__codelineno-39-42" name="__codelineno-39-42" href="#__codelineno-39-42"></a>            <span class="n">undoChoice</span><span class="p">(</span><span class="n">state</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">state</span><span class="p">,</span> <span class="n">choice</span><span class="p">:</span> <span class="n">choice</span><span class="p">)</span>
+<a id="__codelineno-39-43" name="__codelineno-39-43" href="#__codelineno-39-43"></a>        <span class="p">}</span>
+<a id="__codelineno-39-44" name="__codelineno-39-44" href="#__codelineno-39-44"></a>    <span class="p">}</span>
+<a id="__codelineno-39-45" name="__codelineno-39-45" href="#__codelineno-39-45"></a><span class="p">}</span>
 </code></pre></div>
 </div>
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