563. Binary Tree Tilt

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int result = 0;
    public int findTilt(TreeNode root) {
      subSum(root);
      return result;
        
    }
    private int subSum(TreeNode root){
      if(root == null){
        return 0;
      }
      int left = subSum(root.left);
      int right = subSum(root.right);
      
      result += Math.abs(left - right);
      return left + right + root.val;
    }
}