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