【leetcode】Binary Tree Maximum Path Sum

Question ：  

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.

Anwser 1 ：    

/**  * 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 calLen(TreeNode *root, int &len)     {         if (root == NULL)         {             len = 0;             return 0;         }                  if (root->left == NULL && root->right == NULL)         {             len = root->val;             return root->val;         }                  int leftPath, rightPath;         int leftLen;         if (root->left)             leftLen = calLen(root->left, leftPath);         else         {             leftLen = INT_MIN;             leftPath = 0;         }                  int rightLen;         if (root->right)             rightLen = calLen(root->right, rightPath);         else         {             rightLen = INT_MIN;             rightPath = 0;         }                  len = max(max(leftPath, rightPath) + root->val, root->val);         int maxLen = max(root->val, max(leftPath + rightPath + root->val,              max(leftPath + root->val, rightPath + root->val)));                  return max(max(leftLen, rightLen), maxLen);     }          int maxPathSum(TreeNode *root) {         // Start typing your C/C++ solution below         // DO NOT write int main() function         int len;         return calLen(root, len);     } };