LeetCode : 110. Balanced Binary 平衡二叉树

试题
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 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7

Return true.

代码：
本质还是求解树的深度问题

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    boolean flag = true;
    public boolean isBalanced(TreeNode root) {
        findDepth(root);   
        return flag;
    }
    
    public int findDepth(TreeNode root){
        if(root==null) return 0;
        int left = findDepth(root.left);
        int right = findDepth(root.right);
        if(Math.abs(left-right)>1) flag = false;
        return Math.max(left,right)+1;
    }
}