Leetcode -- Binary Tree maximum path sum

Recursion, DFS

The returned value is a pair <int, int>. First indicates the maximum pathsum of the two subtree that does not pass through the current root; second indicates the two subtree, use root-> left and root-> right as the maximum value of the path of the Start Node of the path.

 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 maxPathSum(TreeNode *root) {13         pair<int,int> res = dfs(root);14         return res.first;15     }16     pair<int,int> dfs(TreeNode *root)17     {18         if(root == NULL)19         {20             return make_pair(0,0);21         }22         pair<int,int> left = dfs(root->left);23         pair<int,int> right = dfs(root->right);24         int leftCrossMax = left.first;25         int rightCrossMax = right.first;26         27         int leftMax = left.second > 0?left.second:0;28         int rightMax = right.second > 0?right.second:0;29         30         int maxNoCross = INT_MIN;31         if(root->left != NULL)32         {33             maxNoCross = max(maxNoCross,leftCrossMax);34         }35         if(root->right != NULL)36         {37             maxNoCross = max(maxNoCross,rightCrossMax);38         }39         int maxCross = leftMax+rightMax+root->val;40         int maxSum = max(maxCross,maxNoCross);41         42         int child = max(leftMax,rightMax);43         int maxChild = child > 0?child+root->val:root->val;44         return make_pair(maxSum,maxChild);45     }46 };

 

Leetcode -- Binary Tree maximum path sum