【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 ;
         }

         int left=DFS(root->left);
         int right=DFS(root->right);

         int sum=root->val;
         if(left>) sum+=left;
         if(right>) sum+=right;
         if(maxSum<sum) maxSum=sum;

         return (left>||right>)?root->val+max(left,right):root->val;
     }
 };