Leetcode OJ: Binary Tree Maximum Path Sum

 1 class Solution {
 2 public:
 3     int maxPathSum(TreeNode *root) {
 4         int maxSum = INT_MIN;
 5         maxPathSumImpl(root, maxSum);
 6         return maxSum;
 7     }
 8 private:
 9     int maxPathSumImpl(TreeNode* root, int& maxSum) {
10         if (root == NULL)
11             return 0;
12         int left = maxPathSumImpl(root->left, maxSum);  // 左侧单边
13         int right = maxPathSumImpl(root->right, maxSum);  // 右侧单边
14         int curMax = root->val;
15         if (left > 0)   // 大于零时才有贡献
16             curMax += left;
17         if (right > 0)  // 同上
18             curMax += right;
19         maxSum = max(maxSum, curMax);   // 全局最大
20         int single = root->val + max(0, max(left, right));   // 单边最大
21         return single;
22     }
23 };