[LeetCode] Binary Tree Maximum Path Sum

Given a binary tree, find the maximum path sum.

The path may start and end at any node in the tree.

For example:
Given the below binary tree,

       1      / \     2   3

Return 6.

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int ans;    int maxx(TreeNode *root){        if(root == NULL) return 0;        int s1 = maxx(root -> left);        int s2 = maxx(root -> right);        int num = root -> val;        if(s1 > 0) num += s1;        if(s2 > 0) num += s2;        if(ans < num) ans = num;        return max(root -> val,max(s1,s2) + root -> val);    }    int maxPathSum(TreeNode *root) {       ans = root -> val;       maxx(root);       return ans;    }};