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110.平衡二叉树.java
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110.平衡二叉树.java
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/*
* @lc app=leetcode.cn id=110 lang=java
*
* [110] 平衡二叉树
*
* https://leetcode-cn.com/problems/balanced-binary-tree/description/
*
* algorithms
* Easy (49.05%)
* Likes: 153
* Dislikes: 0
* Total Accepted: 28.4K
* Total Submissions: 57.8K
* Testcase Example: '[3,9,20,null,null,15,7]'
*
* 给定一个二叉树,判断它是否是高度平衡的二叉树。
*
* 本题中,一棵高度平衡二叉树定义为:
*
*
* 一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过1。
*
*
* 示例 1:
*
* 给定二叉树 [3,9,20,null,null,15,7]
*
* 3
* / \
* 9 20
* / \
* 15 7
*
* 返回 true 。
*
* 示例 2:
*
* 给定二叉树 [1,2,2,3,3,null,null,4,4]
*
* 1
* / \
* 2 2
* / \
* 3 3
* / \
* 4 4
*
*
* 返回 false 。
*
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
if (root == null) {
return true;
}
return isBalanced(root.left) && isBalanced(root.right)
&& Math.abs(height(root.left) - height(root.right)) <= 1;
}
private int height(TreeNode root) {
if (root == null) {
return 0;
}
return Math.max(height(root.left), height(root.right)) + 1;
}
}