Balanced Binary Tree leetcode

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.

这道题跟之前一道是一样的 就是找binary tree的深度，用分治法解题。但是要返回的是Boolean值 所以就写一个helper程序 在树平衡时候返回深度 不平衡就返回-1 . 然后用Boolean判定最后返回是否为-1

算法的时间是一次树的遍历O(n)，空间是栈高度O(logn)。

/**
 * 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) {
        return checkBalance(root) != -1;
    }
    public int checkBalance(TreeNode root){
        if (root == null){
            return 0;
        }
        int left = checkBalance(root.left);
        int right = checkBalance(root.right);
        if (left == -1|| right == -1|| Math.abs(left - right) > 1){
            return -1;
        }//如果left或者right不平衡就网上返回-1；
        return Math.max(left, right) + 1;
    }
}