题目链接：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.
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判断一棵树是否是平衡二叉树。BST的递归定义：当一棵树的左右两棵子树的高度只差不超过1，那么该树是平衡二叉树。
用后根遍历求解。先计算两棵子树的高度差。
我的AC代码
public class BalancedBinaryTree {
static boolean ok = true;
public static void main(String[] args) {
TreeNode n1 = new TreeNode(1);
TreeNode n2 = new TreeNode(2);
n1.left = n2;
System.out.println(isBalanced(n1));
}
public static boolean isBalanced(TreeNode root) {
ok = true;
dfs(root);
return ok;
}
public static int dfs(TreeNode root) {
if(root == null || !ok) return 0;
int ha = dfs(root.left);
int hb = dfs(root.right);
if(Math.abs(ha - hb) > 1) ok = false;
return Math.max(ha, hb) + 1;
}
}
LeetCode 110. Balanced Binary Tree 递归求解
原文：http://blog.csdn.net/bruce128/article/details/50724073