【leetcode】Binary Tree Maximum Path Sum

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.

用递归确定每一个节点作为root时，从root出发的最长的路径

在每一次递归中计算maxPath

 1 /**
 2  * Definition for binary tree
 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 maxSum=INT_MIN;
13     int maxPathSum(TreeNode *root) {
14
15         DFS(root);
16         return maxSum;
17     }
18
19     int DFS(TreeNode *root)
20     {
21         if(root==NULL)
22         {
23             return 0;
24         }
25
26         int left=DFS(root->left);
27         int right=DFS(root->right);
28
29         int sum=root->val;
30         if(left>0) sum+=left;
31         if(right>0) sum+=right;
32         if(maxSum<sum) maxSum=sum;
33
34         return (left>0||right>0)?root->val+max(left,right):root->val;
35     }
36 };