【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

 

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxSum=INT_MIN;
    int maxPathSum(TreeNode *root) {
       
        DFS(root);
        return maxSum;
    }
   
    int DFS(TreeNode *root)
    {
        if(root==NULL)
        {
            return 0;
        }
       
        int left=DFS(root->left);
        int right=DFS(root->right);
       
        int sum=root->val;
        if(left>0) sum+=left;
        if(right>0) sum+=right;
        if(maxSum<sum) maxSum=sum;
       
        return (left>0||right>0)?root->val+max(left,right):root->val;
    }
};