[LeetCode]Binary Tree Maximum Path Sum

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
 
class Solution {
public:
    int maxPathSum(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
		int maxLocalMax = root->val;//0 is not correct for all negative values
		int maxSum = DFS(root, maxLocalMax);
		return max(maxSum, maxLocalMax);
    }

	int DFS( TreeNode * root, int& maxLocalMax ) 
	{
		if(root == NULL)
			return 0;
		int left = DFS(root->left, maxLocalMax);
		int right = DFS(root->right, maxLocalMax);
		int localMax = root->val;
		if(left > 0)
			localMax += left;
		if(right > 0)
			localMax += right;
		maxLocalMax = max(localMax, maxLocalMax);//record the max local max
		return max(root->val, max(root->val+left, root->val+right));//return the sum max
	}
};

second time

/**
 * 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 maxPathSumUtil(TreeNode* root, int& maxLocal)
    {
        if(root == NULL) return INT_MIN;
        int left = maxPathSumUtil(root->left, maxLocal);
        int right = maxPathSumUtil(root->right, maxLocal);
        int local = root->val;
        if(left > 0) local += left;
        if(right > 0) local += right;
        maxLocal = max(local, maxLocal);
        return max(max(left, right), 0)+root->val;
    }
    int maxPathSum(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root == NULL) return 0;
        int maxLocal = root->val;
        maxPathSumUtil(root, maxLocal);
        return maxLocal;
    }
};