【树】124. 二叉树中的最大路径和

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int maxPathSum(TreeNode* root) 
13     {
14         int csum;
15         int maxsum = INT_MIN;
16 
17         maxPathSumHelper(root, csum, maxsum);
18 
19         return maxsum;
20     }
21 
22     void maxPathSumHelper(TreeNode *root, int &csum, int &maxsum)
23     {
24         if (NULL == root)
25         {
26             csum = 0;
27             return;
28         }
29 
30         int lsum = 0;
31         int rsum = 0;
32         maxPathSumHelper(root->left, lsum, maxsum);
33         maxPathSumHelper(root->right, rsum, maxsum);
34 
35         csum = std::max(root->val, std::max(root->val + lsum, root->val + rsum));
36         maxsum = std::max(maxsum, std::max(csum, root->val + lsum + rsum));
37     }
38 };