Binary Tree Maximum Path Sum

 

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

 

 

* 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 helper(TreeNode* root,int &ans){
       if(root==NULL)return 0;
       int a=helper(root->left,ans);
       int b=helper(root->right,ans);
       int res=a+b+root->val;
       ans=max(ans,res);
    return max(0,root->val+max(a,b));
}
    int maxPathSum(TreeNode* root) {
        if(root==NULL)return 0;
        if(!root->left&&!root->right)return root->val;
   
        int ans=INT_MIN;
        helper(root,ans);
        return ans;
    }
};