Binary Tree Maximum Path Sum

[124. Binary Tree Maximum Path Sum]

Given a 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.

For example:
Given the below binary tree,

       1
      / \
     2   3

Return 6.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int max = Integer.MIN_VALUE;
    
    public int maxPathSum(TreeNode root) {
        helper(root);
        
        return max;
    }
    
    int helper(TreeNode root) {
        if (root == null) {
            return 0;
        }
        
        int leftSum = Math.max(helper(root.left), 0);
        int rightSum = Math.max(helper(root.right), 0);
        
        max = Math.max(max, root.val + leftSum + rightSum);
        
        return root.val + Math.max(leftSum, rightSum);
    }
}

Hope this helps,
Michael