LeetCode 110. 平衡二叉树

题目链接：​​https://leetcode-cn.com/problems/balanced-binary-tree/​​

给定一个二叉树，判断它是否是高度平衡的二叉树。

1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool isBalanced(TreeNode* root) {
13         return balancedHeight (root) >= 0;
14     }
15     int balancedHeight (TreeNode* root) {
16         if (root == nullptr) return 0; 
17         int left = balancedHeight (root->left);
18         int right = balancedHeight (root->right);
19         if (left < 0 || right < 0 || abs(left - right) > 1) return -1; 
20         return max(left, right) + 1; 
21     }
22 };