LeetCode #124 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 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 maxPathSum(TreeNode* root) {
if(root == NULL) return 0;
int res = root->val;
getMax(root, res);
return res;
}
int getMax(TreeNode *root, int &res){
if(root == NULL) return 0;
int left = getMax(root->left,res);
int right = getMax(root->right, res);
res = max(res, left + right + root->val);
return max(0, max(left, right) + root->val);
}
};