Binary Tree Maximum Path Sum

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxroute(TreeNode* root)
    {
        if(root==NULL)
        return  0;
        int left=maxroute(root->left);
        int right=maxroute(root->right);
        int tmp=left>right?left:right;
       res=(root->val)>res?root->val:res;
       	if(tmp>left+right&&root->val+tmp>res)
			res=root->val+tmp;
		else if(root->val+left+right>res)
             res=root->val+left+right;
		return (tmp>0?root->val+tmp:root->val);
    }
    int maxPathSum(TreeNode* root) {
        
        if (root==NULL)
         return 0;
        if(root->left==NULL&&root->right==NULL)
          return root->val;
          res=root->val;
          int cc= maxroute( root);
        return res;
    }
     int res;
};