LeetCode – Refresh – Balanced Binary Tree

Need a helper function to return the binary tree maximum height. If the return value is -1, it means there is a imbalanced subbranch .

 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 isB(TreeNode *root) {
13         if (!root) return 0;
14         int l = isB(root->left);
15         if (l == -1) return -1;
16         int r = isB(root->right);
17         if (r == -1) return -1;
18         if (fabs(r - l) > 1) return -1;
19         return max(r, l)+1;
20     }
21     bool isBalanced(TreeNode *root) {
22         if (isB(root) == -1) return false;
23         return true;
24     }
25 };