LeetCode 110. Balanced Binary Tree（平衡二叉树）

原题网址：https://leetcode.com/problems/balanced-binary-tree/

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

方法：自顶向下，递归。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    private boolean balanced = true;    private int depth(TreeNode root) {        if (!balanced) return -1;        if (root == null) return 0;        int left = depth(root.left);        int right = depth(root.right);        if (left == -1 || right == -1 || Math.abs(left-right) > 1) {            balanced = false;            return -1;        }        return Math.max(left, right) + 1;    }    public boolean isBalanced(TreeNode root) {        depth(root);        return balanced;    }}