563. Binary Tree Tilt

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

Note:

1. The sum of node values in any subtree won't exceed the range of 32-bit integer.
2. All the tilt values won't exceed the range of 32-bit integer.

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

这道题刚开始的思路有问题，题目也很难一下看懂。如果你把最后累加的只放在迭代函数的返回值，那这样做差值时，值会被抵消！