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/*

Author: King, higuige@gmail.com

Date: Oct 07, 2014

Problem: Balanced Binary Tree

Difficulty: Easy

Source: https://oj.leetcode.com/problems/balanced-binary-tree/

Notes:

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.

Solution: DFS.

*/

/**

* Definition for binary tree

* 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;

return isBalancedRe(root) > -1;

}

public int isBalancedRe(TreeNode root) {

if (root == null) return 0;

int left = isBalancedRe(root.left);

int right = isBalancedRe(root.right);

if (left == -1 || right == -1) return -1;

if (Math.abs(left - right) > 1) return -1;

return Math.max(left, right) + 1;

}

}