leetcode -- Binary Tree Maximum Path Sum

 1 class Solution {
 2 public:
 3     int maxPathSum(TreeNode *root) {
 4         max_sum = root->val;
 5         tt(root);
 6         return max_sum;
 7     }
 8     int tt(TreeNode *root){
 9         if (root == NULL)
10             return 0;
11         int sum = root->val;
12         int l = tt(root->left);
13         int r = tt(root->right);
14         sum += max(l, 0);
15         sum += max(r, 0);
16         max_sum = max(max_sum, sum);
17         return max(l, r) > 0?(root->val + max(l, r)):(root->val);
18     }
19 private:
20     int max_sum;
21 };