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this page</button></div><div class="theme-doc-markdown markdown"><h1>二叉搜索树的第 k 大的节点</h1><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="题目描述">题目描述<a class="hash-link" href="#题目描述" title="Direct link to heading"></a></h2><p>给定一棵二叉搜索树，请找出其中第 k 大的节点。</p><p>示例 1：</p><div class="codeBlockContainer_I0IT theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-text codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token plain">输入: root = [3,1,4,null,2], k = 1</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 3</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> / \</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 1 4</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> \</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 2</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">输出: 4</span><br></span></code></pre><button type="button" aria-label="Copy code to clipboard" title="Copy" class="copyButton_eDfN clean-btn"><span class="copyButtonIcons_W9eQ" aria-hidden="true"><svg class="copyButtonIcon_XEyF" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_i9w9" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div><p>示例 2：</p><div class="codeBlockContainer_I0IT theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-text codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token plain">输入: root = [5,3,6,2,4,null,null,1], k = 3</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 5</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> / \</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 3 6</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> / \</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 2 4</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> /</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 1</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">输出: 4</span><br></span></code></pre><button type="button" aria-label="Copy code to clipboard" title="Copy" class="copyButton_eDfN clean-btn"><span class="copyButtonIcons_W9eQ" aria-hidden="true"><svg class="copyButtonIcon_XEyF" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_i9w9" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="解题基本知识">解题基本知识<a class="hash-link" href="#解题基本知识" title="Direct link to heading"></a></h2><p>二叉搜索树（Binary Search Tree）又名二叉查找树、二叉排序树。它是一棵空树，或者是具有下列性质的二叉树： 若它的左子树不空，则左子树上所有结点的值均小于它的根结点的值； 若它的右子树不空，则右子树上所有结点的值均大于它的根结点的值； 它的左、右子树也分别为二叉排序树。</p><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="解法一-递归">解法一： 递归<a class="hash-link" href="#解法一-递归" title="Direct link to heading"></a></h2><p><a href="https://codesandbox.io/s/erchasousuoshudedi-k-dadejiedian-vfpbh?file=/index.html" target="_blank" rel="noopener noreferrer">在线链接</a></p><p>利用二叉搜索树的特性进行中序遍历。先遍历左节点，然后根节点，最后遍历右节点，得到的是一个递增序列，那么序列的倒序为递减序列。因此这道题我们可以转变为求二叉搜索树中序遍历倒序的第 k 个数。</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/15681693/130164388-85e96093-9336-4174-b139-59e83d972a20.png" alt="解法图示" class="img_E7b_"></p><div class="codeBlockContainer_I0IT language-javascript theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-javascript codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">/**</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * Definition for a binary tree node.</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * function TreeNode(val) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.val = val;</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.left = this.right = null;</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * }</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">/**</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @param {TreeNode} root</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @param {number} k</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @return {number}</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">kthLargest</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">root</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> k</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">let</span><span class="token plain"> res </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 初始化返回值</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 因为需要倒序第 k 个，所以处理是右节点，根节点，然后左节点</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">dfs</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token operator" style="color:#393A34">!</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 如果当前节点为 null，本轮处理结束</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">dfs</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">right</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 开始处理右节点</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">k </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// k 值 为 0，代表已经处理的节点超过目标节点，本轮处理结束</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token operator" style="color:#393A34">--</span><span class="token plain">k </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 当 k 值 减 1 为 0，表示已经到了我们想要的 k 大 节点，保存当前值</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> res </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> root</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">val</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">dfs</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">left</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 处理左节点</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">dfs</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 从初始化节点开始处理</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> res</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><button type="button" aria-label="Copy code to clipboard" title="Copy" class="copyButton_eDfN clean-btn"><span class="copyButtonIcons_W9eQ" aria-hidden="true"><svg class="copyButtonIcon_XEyF" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_i9w9" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="复杂度分析">复杂度分析：<a class="hash-link" href="#复杂度分析" title="Direct link to heading"></a></h3><ul><li>时间复杂度 O(N)：无论 k 的值大小，递归深度都为 N，占用 O(N) 时间。</li><li>空间复杂度 O(N)：无论 k 的值大小，递归深度都为 N，占用 O(N) 空间。</li></ul><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="解法二-迭代">解法二： 迭代<a class="hash-link" href="#解法二-迭代" title="Direct link to heading"></a></h2><p><a href="https://codesandbox.io/s/hzfe-suan-fa-er-cha-sou-suo-shu-de-di-k-da-de-jie-dian-die-dai-kq565?file=/index.html" target="_blank" rel="noopener noreferrer">在线链接</a></p><p>思路还是二叉树的中序遍历，利用栈的方式进行遍历。</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/15681693/137573367-0855a00c-7406-4837-86d4-38d73f9c7bb7.png" alt="解法图示" class="img_E7b_"></p><div class="codeBlockContainer_I0IT language-javascript theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-javascript codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">/**</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * Definition for a binary tree node.</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * function TreeNode(val) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.val = val;</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.left = this.right = null;</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * }</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">/**</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @param {TreeNode} root</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @param {number} k</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @return {number}</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">var</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">kthLargest</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">root</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> k</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token operator" style="color:#393A34">!</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 声明储存栈</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> stack </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 判断当前栈否有节点和当前遍历节点位置</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">while</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">stack</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">length</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">while</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 往栈里添加当前节点，同时切换为右节点处理</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> stack</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">push</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> root </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> root</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">right</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 取出当前栈顶元素，根据添加的顺序，当前元素是栈内最大的</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> cur </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> stack</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">pop</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> k</span><span class="token operator" style="color:#393A34">--</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">k </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> cur</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">val</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 切换为左节点处理</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> root </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> cur</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">left</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><button type="button" aria-label="Copy code to clipboard" title="Copy" class="copyButton_eDfN clean-btn"><span class="copyButtonIcons_W9eQ" aria-hidden="true"><svg class="copyButtonIcon_XEyF" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_i9w9" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div><ul><li>时间复杂度 O(N)：需要遍历整棵树一次，复杂度为 O(N)</li><li>空间复杂度 O(N)：需要额外空间栈进行储存树，复杂度为 O(N)</li></ul><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="参考资料">参考资料<a class="hash-link" href="#参考资料" title="Direct link to heading"></a></h3><ol><li><a href="https://book.douban.com/subject/6966465/" target="_blank" rel="noopener noreferrer">剑指 offer</a></li></ol></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><div class="pagination-nav__item"><a class="pagination-nav__link" href="/awesome-interview/book3/coding-arr-to-tree"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">编码：将列表还原为树状结构</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book3/topic-white-screen-optimization"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">综合：如何减少白屏的时间</div></a></div></nav></div></div><div class="col col--3"><div class="tableOfContents_cNA8 thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#题目描述" class="table-of-contents__link toc-highlight">题目描述</a></li><li><a href="#解题基本知识" class="table-of-contents__link toc-highlight">解题基本知识</a></li><li><a href="#解法一-递归" class="table-of-contents__link toc-highlight">解法一： 递归</a><ul><li><a href="#复杂度分析" class="table-of-contents__link toc-highlight">复杂度分析：</a></li></ul></li><li><a href="#解法二-迭代" class="table-of-contents__link toc-highlight">解法二： 迭代</a><ul><li><a href="#参考资料" 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