DiffSum

Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes' tilt.

Example

Input:

         1
       /   \
      2     3

Output:
 1

Explanation:

Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

Code

class Solution {
    private static class ResultType {
        int sum, diffSum;
        public ResultType(int sum, int diffSum) {
            this.sum = sum;
            this.diffSum = diffSum;
        }
    }

    public int findTilt(TreeNode root) {
        if (root == null) {
            return 0;
        }

        ResultType res = helper(root);

        return res.diffSum;
    }

    private ResultType helper(TreeNode root) {
        if (root == null) {
            return new ResultType(0, 0);
        }

        ResultType left = helper(root.left);
        ResultType right = helper(root.right);

        int diffSum = Math.abs(left.sum - right.sum) + left.diffSum + right.diffSum; 

        return new ResultType(root.val + left.sum + right.sum, diffSum);
    }
}