110. 平衡二叉树
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:
输入:root = [3,9,20,null,null,15,7]
输出:true
示例 2:
输入:root = [1,2,2,3,3,null,null,4,4]
输出:false
示例 3:
输入:root = []
输出:true
提示:
树中的节点数在范围 [0, 5000] 内
-104 <= Node.val <= 104
来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/balanced-binary-tree
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分析
分析参考:
https://github.com/youngyangyang04/leetcode-master/blob/master/problems/0110.%E5%B9%B3%E8%A1%A1%E4%BA%8C%E5%8F%89%E6%A0%91.md
题解(Java)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
return getHeight(root) != -1;
}
public int getHeight(TreeNode root) {
if (root == null) return 0;
int leftHeight = getHeight(root.left);
if (leftHeight == -1) return -1;
int rightHeight = getHeight(root.right);
if (rightHeight == -1) return -1;
if (Math.abs(leftHeight - rightHeight) > 1) {
return -1;
}
return 1 + Math.max(leftHeight, rightHeight);
}
}