# Balanced Binary Tree

## Problem

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.

## Example

Given binary tree A={3,9,20,#,#,15,7}, B={3,#,20,15,7}

A)  3            B)    3
/ \                  \
9  20                 20
/  \                / \
15   7              15  7

The binary tree A is a height-balanced binary tree, but B is not.

## Code - Java

/**
* Definition of TreeNode:
* public class TreeNode {
*   public int val;
*   public TreeNode left, right;
*   public TreeNode(int val) {
*     this.val = val;
*     this.left = this.right = null;
*   }
* }
*/
public class Solution {
/**
* @param root: The root of binary tree.
* @return: True if this Binary tree is Balanced, or false.
*/
public boolean isBalanced(TreeNode root) {
return balanced(root) != -1;
}

private int balanced(TreeNode root) {
if (root == null) {
return 0;
}

int left = balanced(root.left);
int right = balanced(root.right);

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

if (Math.abs(left - right) <= 1) {
return Math.max(left, right) + 1;
} else {
return -1;
}
}
}