【leetcode】110.Balanced Binary Tree

题目要求：

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.

即给定一颗二叉树，判断它是不是平衡的

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public boolean isBalanced(TreeNode root) {         if(root==null)        {            return true;        }        int l = depth(root.left);        int r = depth(root.right);        if(l-r>1||r-l>1)        {            return false;        }        return isBalanced(root.left)&&isBalanced(root.right);    }     //辅助函数，用来求二叉树的深度    public int depth(TreeNode root)    {        if(root==null)        {            return 0;        }        int left = depth(root.left);        int right = depth(root.right);        return 1+(left>right?left:right);    }}