balanced-binary-tree
（1过）
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.
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 。
给定二叉树 [1,2,2,3,3,null,null,4,4]
1 / \ 2 2 / \ 3 3 / \ 4 4
返回 false 。
我的解法：
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class BalancedBinaryTree { boolean flag = true; public boolean isBalanced(TreeNode root) { height(root); return flag; } private int height(TreeNode root) { if(root == null) { return 0; } int left = height(root.left); int right = height(root.right); if (Math.abs(left -right) >1) { flag = false; } return Math.max(left,right)+1; }}