Given a binary tree, find the maximum path sum. The path may start and end at any node in the tree. http://www.leetcode.com/onlinejudge

leetcode_binary_tree_maximum_path_sum.cpp

#include <algorithm>
using namespace std;

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

#define MIN_INT -0x7fffffff
class Solution {
public:
    void max_pathsum_(int& ret, int& pathSum, TreeNode* root) {
        if (root == NULL) {
            ret = MIN_INT;
            pathSum = 0;
            return;
        }
        int left_ret;
        int left_pathSum;
        int right_ret;
        int right_pathSum;
        max_pathsum_(left_ret, left_pathSum, root->left);
        max_pathsum_(right_ret, right_pathSum, root->right);
        pathSum = max(max(left_pathSum, right_pathSum) + root->val, 0);
        ret = max(max(left_ret, right_ret), left_pathSum + right_pathSum + root->val);
    }

    int maxPathSum(TreeNode *root) {
        int ret = 0;
        int pathSum = 0;
        max_pathsum_(ret, pathSum, root);
        return ret;
    }
};