Maximum Subtree

public class Solution {
/*
* @param root: the root of binary tree
* @return: the maximum weight node
*/
public TreeNode result = null;
public int maximum_weight = Integer.MIN_VALUE;

public TreeNode findSubtree(TreeNode root) {
    // Write your code here
    helper(root);
    
    return result;
}

public int helper(TreeNode root) {
    if (root == null) {
        return 0;
    }
    int left_weight = helper(root.left);
    int right_weight = helper(root.right);

    if (result == null || left_weight + right_weight + root.val > maximum_weight) {
        maximum_weight = left_weight + right_weight + root.val;
        result = root;
    }

    return left_weight + right_weight + root.val;
}

}