LeetCode Binary Tree Maximum Path Sum

Given a binary tree, find the maximum path sum.

The path may start and end at any node in the tree.

For example:
Given the below binary tree,

       1
      / 
     2   3

Return 6.

/**
 * Definition for binary tree
 * 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) {
        if (root == null) {
            return 0;
        }
        maxSum(root);
        return max;
    }

    private int  maxSum(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftSum=0;
        int rightSum=0;
        int val=root.val;
        if (root.left != null) {
            leftSum = maxSum(root.left);
            if (leftSum > 0) {
                val = val + leftSum;
            }
        }

        if (root.right != null) {
            rightSum = maxSum(root.right);
            if (rightSum > 0) {
                val = val + rightSum;
            }
        }

        if (val > max) {
            max = val;
        }

        return Math.max(root.val, Math.max(root.val + leftSum, root.val + rightSum));


    }
}