124. Binary Tree Maximum Path Sum | Leetcode Solution

 124. Binary Tree Maximum Path Sum | Leetcode Solution

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.

The path sum of a path is the sum of the node's values in the path.

Given the root of a binary tree, return the maximum path sum of any non-empty path.

 

Example 1:

Input: root = [1,2,3]
Output: 6
Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.

Example 2:

Input: root = [-10,9,20,null,null,15,7]
Output: 42
Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.

 

Constraints:

• The number of nodes in the tree is in the range [1, 3 * 104].
• -1000 <= Node.val <= 1000

/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}

 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}

 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}

 * };

 */

class Solution {

public:

    int ans=INT_MIN;

    unordered_map<TreeNode*,int>m;

    int helper(TreeNode* root){

        if(root==NULL)return 0;

      int left=  max(0,helper(root->left));

       int right= max(0,helper(root->right));

        ans=max(root->val+left+right,ans);

        return max(left,right)+root->val;

    }

    

    

    int maxPathSum(TreeNode* root) {

        helper(root);

        return ans;

        

    }

};