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class="docItemContainer_vinB"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Xlws" aria-label="breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a class="breadcrumbs__link" href="/awesome-interview/">🏠</a></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><span class="breadcrumbs__link" itemprop="item name">模拟题一</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="item name">算法：平衡二叉树</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_jdIR theme-doc-toc-mobile tocMobile_TmEX"><button type="button" class="clean-btn tocCollapsibleButton_Fzxq">On this page</button></div><div class="theme-doc-markdown markdown"><h1>平衡二叉树</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>输入一棵二叉树的根节点，判断该树是不是平衡二叉树。如果某二叉树中任意节点的左右子树的深度相差不超过 1，那么它就是一棵平衡二叉树。</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">给定二叉树 [3, 9, 20, null, null, 15, 7]</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></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"> 9 20</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"> 15 7</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">返回 true。</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">给定二叉树 [1,2,2,3,3,null,null,4,4]</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></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"> / \</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> 2 2</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 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"> 4 4</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">返回 false。</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>限制：0 <= 树的结点个数 <= 10000</p><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="基本知识点">基本知识点<a class="hash-link" href="#基本知识点" title="Direct link to heading"></a></h2><p>二叉树的每个节点最多有两个子节点，平衡二叉树中任意一个节点的左右子树高度相差不能大于 1，满二叉树和完全二叉树都是平衡二叉树，普通二叉树有可能是平衡二叉树。</p><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="题解">题解<a class="hash-link" href="#题解" title="Direct link to heading"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="解法一">解法一<a class="hash-link" href="#解法一" title="Direct link to heading"></a></h3><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="思路">思路<a class="hash-link" href="#思路" title="Direct link to heading"></a></h4><p>若想判断二叉树是不是平衡二叉树，只需要判断左右子树的高度差是不是不超过 1 即可。同时，要满足一个树是平衡二叉树，它的子树也必须是平衡二叉树。我们可以从根结点开始，通过递归来求得子树的高度，以及子树是否是平衡二叉树，以此来结合判断二叉树是否是平衡二叉树。</p><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="代码">代码<a class="hash-link" href="#代码" title="Direct link to heading"></a></h4><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, left, right) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.val = (val === undefined ? 0 : val)</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.left = (left === undefined ? null : left)</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.right = (right === undefined ? null : right)</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"> * @return {boolean}</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">isBalanced</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 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 plain">root </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 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 boolean" style="color:#36acaa">true</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><span class="token keyword control-flow" style="color:#00009f">else</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">return</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 known-class-name class-name">Math</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">abs</span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">height</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 plain"> </span><span class="token operator" style="color:#393A34">-</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">height</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 operator" style="color:#393A34"><=</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token plain"> </span><span class="token operator" 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">isBalanced</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 plain"> </span><span class="token operator" 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">isBalanced</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 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 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><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></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">height</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 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 plain">root </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 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 plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</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">return</span><span class="token plain"> </span><span class="token known-class-name class-name">Math</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">max</span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">height</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 function" style="color:#d73a49">height</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 operator" style="color:#393A34">+</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</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 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><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="时间复杂度分析">时间复杂度分析<a class="hash-link" href="#时间复杂度分析" title="Direct link to heading"></a></h4><p>该方法最坏的情况是每个父节点都只有一个子节点，这样树的高度时间复杂度为 O(n)，即“链表”的长度。而第 d 层调用 <code>height</code> 函数的时间复杂度是 O(d)，所以整体的时间复杂度为高度时间复杂度 <!-- -->*<!-- --> 调用 <code>height</code> 函数的时间复杂度，即 O(n^2)。</p><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="空间复杂度分析">空间复杂度分析<a class="hash-link" href="#空间复杂度分析" title="Direct link to heading"></a></h4><p>空间复杂度取决于递归调用的层数，不会超过 n 层，所以空间复杂度是 O(n)。</p><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="解法二">解法二<a class="hash-link" href="#解法二" title="Direct link to heading"></a></h3><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="思路-1">思路<a class="hash-link" href="#思路-1" title="Direct link to heading"></a></h4><p>上面的方法是自顶而下的，这样其实就会导致每层的高度都要重复计算。那么，我们可以使用后序遍历，这样每个节点的高度就能根据前面的结果算出来。</p><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="代码-1">代码<a class="hash-link" href="#代码-1" title="Direct link to heading"></a></h4><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, left, right) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.val = (val === undefined ? 0 : val)</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.left = (left === undefined ? null : left)</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * this.right = (right === undefined ? null : right)</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"> * @return {boolean}</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">isBalanced</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 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">return</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">height</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 operator" style="color:#393A34">!=</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">-</span><span class="token number" style="color:#36acaa">1</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><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></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">height</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 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 plain">root </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 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 plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></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"> left </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">height</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><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"> right </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">height</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><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></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">left </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">-</span><span class="token number" style="color:#36acaa">1</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> right </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">-</span><span class="token number" style="color:#36acaa">1</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> </span><span class="token known-class-name class-name">Math</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">abs</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">left </span><span class="token operator" style="color:#393A34">-</span><span class="token plain"> right</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">></span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</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">return</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">-</span><span class="token number" style="color:#36acaa">1</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" style="display:inline-block"></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 known-class-name class-name">Math</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">max</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">left</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> right</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">+</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</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><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="时间复杂度分析-1">时间复杂度分析<a class="hash-link" href="#时间复杂度分析-1" title="Direct link to heading"></a></h4><p>由于是后序遍历，每个节点只会被调用 1 次，所以，该方法的时间复杂度是 O(n)。</p><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="空间复杂度分析-1">空间复杂度分析<a class="hash-link" href="#空间复杂度分析-1" title="Direct link to heading"></a></h4><p>空间复杂度取决于递归调用的层数，不会超过 n 层，所以空间复杂度是 O(n)。</p></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/book1/coding-promise"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">编码：实现一个符合 Promises/A+ 规范的 Promise</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book1/topic-enter-url-display-xx"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">综合：浏览器从输入网址到页面展现的过程</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="#基本知识点" class="table-of-contents__link toc-highlight">基本知识点</a></li><li><a href="#题解" class="table-of-contents__link toc-highlight">题解</a><ul><li><a href="#解法一" class="table-of-contents__link toc-highlight">解法一</a><ul><li><a href="#思路" class="table-of-contents__link toc-highlight">思路</a></li><li><a href="#代码" class="table-of-contents__link toc-highlight">代码</a></li><li><a href="#时间复杂度分析" class="table-of-contents__link toc-highlight">时间复杂度分析</a></li><li><a href="#空间复杂度分析" class="table-of-contents__link toc-highlight">空间复杂度分析</a></li></ul></li><li><a href="#解法二" class="table-of-contents__link toc-highlight">解法二</a><ul><li><a href="#思路-1" class="table-of-contents__link toc-highlight">思路</a></li><li><a href="#代码-1" class="table-of-contents__link toc-highlight">代码</a></li><li><a href="#时间复杂度分析-1" class="table-of-contents__link 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