题目：

1Given a binary tree, determine if it is height-balanced.
2
3For 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.
4

思路：

• 题目的大意是【判断一个二叉树是不是平衡二叉树
• 首先了解平衡二叉树的概念：只有根节点是，或者左右节点的深度只差不大于1
• 因为二叉树本身是一个递归的结构，所以二叉树的好多问题使可以用递归解决的，考虑root和root.left以及root.right的关系

代码：

1/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */
2public class Solution {
3    public boolean isBalanced(TreeNode root) {
4        if(root == null){
5            return true;
6        }
7        if(Math.abs(depth(root.left)-depth(root.right)) > 1){
8            return false;
9        }
10        return isBalanced(root.left)&&isBalanced(root.right);
11    }
12    public int depth(TreeNode root){
13        if(root == null){
14            return 0;
15        }
16        return 1+Math.max(depth(root.left),depth(root.right));
17    }
18}