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 does not need to go through the root.

For example: Given the below binary tree,

   1
  / \
 2   3

Return 6.

Solution:

/**
 * 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;
    }
    public int helper(TreeNode root) {
        if(root==null) return 0;
        int left = Math.max(0, helper(root.left));
        int right = Math.max(0, helper(root.right));
        max = Math.max(max, left+right+root.val);
        return Math.max(left, right)+root.val;
    }
}