leetcode:Balanced Binary Tree

 1 /**
 2  * Definition for binary tree
 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    int flag=true;
13     int dfs(TreeNode *root)
14     {
15          if(root==NULL) return true;
16          int h1,h2;
17          if(root->left==NULL) h1=0;
18          else h1=dfs(root->left);
19          if(root->right==NULL) h2=0;
20          else h2=dfs(root->right);
21          if(abs(h1-h2)>1) flag=0;
22          return max(h1,h2)+1;
23     }
24     bool isBalanced(TreeNode *root) {
25         dfs(root);
26         return flag;
27     }
28 };