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‎README.adoc

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@@ -4659,14 +4659,14 @@ TIP: **公众号的微信号是: `jikerizhi`**。__因为众所周知的原因
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//|{doc_base_url}/0661-image-smoother.adoc[题解]
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//|Easy
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//|
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//
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//|{counter:codes}
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//|{leetcode_base_url}/maximum-width-of-binary-tree/[662. Maximum Width of Binary Tree^]
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//|{source_base_url}/_0662_MaximumWidthOfBinaryTree.java[Java]
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//|{doc_base_url}/0662-maximum-width-of-binary-tree.adoc[题解]
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//|Medium
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//|
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//
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|{counter:codes}
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|{leetcode_base_url}/maximum-width-of-binary-tree/[662. Maximum Width of Binary Tree^]
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|{source_base_url}/_0662_MaximumWidthOfBinaryTree.java[Java]
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|{doc_base_url}/0662-maximum-width-of-binary-tree.adoc[题解]
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|Medium
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|
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//|{counter:codes}
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//|{leetcode_base_url}/equal-tree-partition/[663. Equal Tree Partition^]
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//|{source_base_url}/_0663_EqualTreePartition.java[Java]

‎docs/0662-maximum-width-of-binary-tree.adoc

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[#0662-maximum-width-of-binary-tree]
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= 662. Maximum Width of Binary Tree
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= 662. 二叉树最大宽度
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{leetcode}/problems/maximum-width-of-binary-tree/[LeetCode - Maximum Width of Binary Tree^]
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https://leetcode.cn/problems/maximum-width-of-binary-tree/[LeetCode - 662. 二叉树最大宽度 ^]
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Given a binary tree, write a function to get the maximum width of the given tree. The width of a tree is the maximum width among all levels. The binary tree has the same structure as a *full binary tree*, but some nodes are null.
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给你一棵二叉树的根节点 `root` ，返回树的 *最大宽度* 。
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The width of one level is defined as the length between the end-nodes (the leftmost and right most non-null nodes in the level, where the `null` nodes between the end-nodes are also counted into the length calculation.
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树的 *最大宽度* 是所有层中最大的 *宽度* 。
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*Example 1:*
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每一层的 *宽度* 被定义为该层最左和最右的非空节点（即，两个端点）之间的长度。将这个二叉树视作与满二叉树结构相同，两端点间会出现一些延伸到这一层的 `null` 节点，这些 `null` 节点也计入长度。
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[subs="verbatim,quotes,macros"]
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----
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*Input:*
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题目数据保证答案将会在 *32 位* 带符号整数范围内。
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1
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/ \
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3 2
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/ \ \
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5 3 9
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*示例 1：*
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*Output:* 4
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*Explanation:* The maximum width existing in the third level with the length 4 (5,3,null,9).
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----
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image::images/0662-01.jpg[{image_attr}]
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*Example 2:*
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....
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输入：root = [1,3,2,5,3,null,9]
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输出：4
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解释：最大宽度出现在树的第 3 层，宽度为 4 (5,3,null,9) 。
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....
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[subs="verbatim,quotes,macros"]
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----
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*Input:*
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*示例 2：*
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1
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/
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3
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/ \
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5 3
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image::images/0662-02.jpg[{image_attr}]
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*Output:* 2
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*Explanation:* The maximum width existing in the third level with the length 2 (5,3).
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----
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....
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输入：root = [1,3,2,5,null,null,9,6,null,7]
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输出：7
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解释：最大宽度出现在树的第 4 层，宽度为 7 (6,null,null,null,null,null,7) 。
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....
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*Example 3:*
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*示例 3：*
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[subs="verbatim,quotes,macros"]
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----
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*Input:*
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image::images/0662-03.jpg[{image_attr}]
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1
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/ \
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3 2
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/
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5
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....
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输入：root = [1,3,2,5]
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输出：2
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解释：最大宽度出现在树的第 2 层，宽度为 2 (3,2) 。
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....
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*Output:* 2
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*Explanation:* The maximum width existing in the second level with the length 2 (3,2).
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----
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*提示：*
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*Example 4:*
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* 树中节点的数目范围是 `[1, 3000]`
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* `+-100 <= Node.val <= 100+`
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[subs="verbatim,quotes,macros"]
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----
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*Input:*
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1
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/ \
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3 2
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/ \
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5 9
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/ \
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6 7
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*Output:* 8
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*Explanation:* The maximum width existing in the fourth level with the length 8 (6,null,null,null,null,null,null,7).
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== 思路分析
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使用伪节点进行广度优先遍历超时！
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----
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从上到下，每个节点都有一个编号，如果父节点是 `x`，则左节点是 `2x`，而右节点是 `2x+1`，因为父节点可以这个节点编号传递下去，这样不需要关注空节点。把每一层节点放入到一个队列中，尾部节点的编号减去头部节点编号再加 1 就是每层的宽度。
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*Note:* Answer will in the range of 32-bit signed integer.
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image::images/0662-10.png[{image_attr}]
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还有一个深度优先遍历的解法：
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image::images/0662-11.png[{image_attr}]
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[[src-0662]]
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[tabs]
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====
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一刷（超时）::
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+
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--
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[{java_src_attr}]
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----
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include::{sourcedir}/_0662_MaximumWidthOfBinaryTree.java[tag=answer]
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----
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--
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一刷::
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+
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--
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[{java_src_attr}]
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----
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include::{sourcedir}/_0662_MaximumWidthOfBinaryTree_1.java[tag=answer]
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----
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--
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// 二刷::
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// +
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// --
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// [{java_src_attr}]
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// ----
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// include::{sourcedir}/_0662_MaximumWidthOfBinaryTree_2.java[tag=answer]
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// ----
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// --
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====
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== 参考资料
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. https://leetcode.cn/problems/maximum-width-of-binary-tree/solutions/1776589/er-cha-shu-zui-da-kuan-du-by-leetcode-so-9zp3/[662. 二叉树最大宽度 - 官方题解^]
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. https://leetcode.cn/problems/maximum-width-of-binary-tree/solutions/1779284/by-muse-77-7hwf/[662. 二叉树最大宽度 - 【爪哇缪斯】图解LeetCode^]
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‎docs/images/0662-01.jpg

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‎docs/images/0662-02.jpg

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‎docs/images/0662-03.jpg

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‎docs/images/0662-10.png

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‎docs/images/0662-11.png

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‎docs/index.adoc

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// include::0661-image-smoother.adoc[leveloffset=+1]
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// include::0662-maximum-width-of-binary-tree.adoc[leveloffset=+1]
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include::0662-maximum-width-of-binary-tree.adoc[leveloffset=+1]
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// include::0663-equal-tree-partition.adoc[leveloffset=+1]
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‎logbook/202503.adoc

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|{doc_base_url}/0011-container-with-most-water.adoc[题解]
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|✅ 双指针
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|{counter:codes}
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|{counter:codes2503}
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|{leetcode_base_url}/remove-element/[27. 移除元素^]
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|{doc_base_url}/0027-remove-element.adoc[题解]
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|✅ 快慢指针。慢指针记录满足条件的长度，快指针指向需要处理的元素。
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|{counter:codes}
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|{counter:codes2503}
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|{leetcode_base_url}/trapping-rain-water/[42. 接雨水^]
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|{doc_base_url}/0042-trapping-rain-water.adoc[题解]
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|❌ 使用单调栈没写出来。使用单调栈，需 `h × w`，不能只看头顶的容量。使用左右双指针夹逼代码更简单，只需要计算头顶的容量即可。
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|{counter:codes}
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|{counter:codes2503}
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|{leetcode_base_url}/edit-distance/[72. 编辑距离^]
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|{doc_base_url}/0072-edit-distance.adoc[题解]
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|✅ 动态规划。思考如何进一步优化成一维数组？
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|{counter:codes2503}
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|{leetcode_base_url}/maximum-width-of-binary-tree/[662. Maximum Width of Binary Tree^]
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|{doc_base_url}/0662-maximum-width-of-binary-tree.adoc[题解]
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|⭕️ 添加虚拟节点的做法超时。看答案给节点加编号通过。
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|===
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截止目前，本轮练习一共完成 {codes2503} 道题。

‎src/main/java/com/diguage/algo/leetcode/_0662_MaximumWidthOfBinaryTree.java

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package com.diguage.algo.leetcode;
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import com.diguage.algo.util.TreeNode;
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import java.util.Deque;
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import java.util.LinkedList;
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public class _0662_MaximumWidthOfBinaryTree {
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// tag::answer[]
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/**
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* 通过 94 / 116 个测试用例，但超时了。
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*
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* @author D瓜哥 · https://www.diguage.com
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* @since 2025-04-20 21:13:45
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*/
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public int widthOfBinaryTree(TreeNode root) {
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final TreeNode DUMMY = new TreeNode(Integer.MAX_VALUE);
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Deque<TreeNode> queue = new LinkedList<>();
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queue.offer(root);
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int result = 0;
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while (!queue.isEmpty()) {
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int size = queue.size();
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result = Math.max(result, size);
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for (int i = 0; i < size; i++) {
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TreeNode node = queue.poll();
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if (node.left != null) {
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queue.offer(node.left);
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} else {
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queue.offer(DUMMY);
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}
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if (node.right != null) {
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queue.offer(node.right);
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} else {
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queue.offer(DUMMY);
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}
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}
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while (!queue.isEmpty() && queue.peek() == DUMMY) {
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queue.poll();
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}
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while (!queue.isEmpty() && queue.peekLast() == DUMMY) {
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queue.pollLast();
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}
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}
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return result;
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}
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// end::answer[]
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}

‎src/main/java/com/diguage/algo/leetcode/_0662_MaximumWidthOfBinaryTree_1.java

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package com.diguage.algo.leetcode;
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import com.diguage.algo.util.TreeNode;
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import java.util.Deque;
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import java.util.LinkedList;
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public class _0662_MaximumWidthOfBinaryTree_1 {
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// tag::answer[]
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/**
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* @author D瓜哥 · https://www.diguage.com
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* @since 2025-04-20 21:37:22
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*/
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public int widthOfBinaryTree(TreeNode root) {
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Deque<Pair<TreeNode, Integer>> nodes = new LinkedList<>();
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int result = 0;
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nodes.add(new Pair<>(root, 1));
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while (!nodes.isEmpty()) {
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result = Math.max(result,
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nodes.getLast().value - nodes.getFirst().value + 1);
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int size = nodes.size();
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for (int i = 0; i < size; i++) {
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Pair<TreeNode, Integer> pair = nodes.poll();
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if (pair.key.left != null) {
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nodes.offer(new Pair<>(pair.key.left, pair.value * 2));
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}
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if (pair.key.right != null) {
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nodes.offer(new Pair<>(pair.key.right, pair.value * 2 + 1));
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}
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}
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}
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return result;
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}
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private static class Pair<K, V> {
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K key;
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V value;
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public Pair(K key, V value) {
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this.key = key;
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this.value = value;
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}
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}
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// end::answer[]
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}

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