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.

题意：判断一棵二叉树是否为平衡二叉树

平衡二叉树或者是一颗空树，或者是它的左右子树都是平衡二叉树，且左子树和右子树高度之差的绝对值不超过1

/**
 * 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) {
         return (getHeight(root) != -1);
    }
    public int getHeight(TreeNode root) {
		if (root == null) {
			return 0;
		}
		int leftHeight = getHeight(root.left);
		if (leftHeight == -1) {
			return -1;
		}
		int rightHeight = getHeight(root.right);
		if (rightHeight == -1) {
			return -1;
		}
		if (Math.abs(leftHeight - rightHeight) > 1) {
			return -1;
		} else {
			return 1+Math.max(leftHeight, rightHeight);
		}
	}
}