# 124. Binary Tree Maximum Path Sum

## 刷题内容

• https://leetcode.com/problems/binary-tree-maximum-path-sum/

Given a non-empty binary tree, find the maximum path sum.

For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and does not need to go through the root.

Example 1:

Input: [1,2,3]

1
/ \
2   3

Output: 6
Example 2:

Input: [-10,9,20,null,null,15,7]

-10
/ \
9  20
/  \
15   7

Output: 42


˼· **- ʱ�临�Ӷ�: O(N)*- �ռ临�Ӷ�: O(1)***

�����뵽内容描述DP��ʱ�临�Ӷ�ΪO(n^2)内容描述���Ƕ�������ֻ内容描述内容描述����ˣ����ǿ����ø��Ż����㷨�������ú内容描述������Ȼ���¼������ڵ�����·���� ans�Ƚϡ����� max(l,r) 内容描述ڵ��ֵ��

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int ans = INT_MIN;
int travel(TreeNode* root)
{
if(!root)
return 0;
int l = travel(root ->left);
int r = travel(root ->right);
if(l < 0)
l = 0;
if(r < 0)
r = 0;
int temp = r + l + root ->val;
ans = max(ans,temp);
return max(l,r) + root ->val;
}
int maxPathSum(TreeNode* root) {
travel(root);
if(ans == INT_MIN)
return 0;
return ans;
}
};