LeetCode 563 Binary Tree Tilt

题目：

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.

题目链接

题意：

给一个二叉树，让求出整棵树的tilt，单个节点的tilt的定义为左子数的val总和与右子树val总和的差的绝对值，整棵树的tilt定义为所有节点的tilt的总和。

为了实现求和，我另写了一个函数，对于每一个节点而言：

sum(node) = sum(node->left) + sum(node->right) + node->val;

从而写出递归函数 ，在每次递归时，计算sum(left)与sum(right)的绝对差，并加到ans中，

在主函数中返回ans。

代码如下：

class Solution {public:    int ans = 0;    int sum(TreeNode* node) {        if (node == NULL) return 0;                int sumL = sum(node->left);        int sumR = sum(node->right);                ans += abs(sumL - sumR);                return sumL + sumR + node->val;    }        int findTilt(TreeNode* root) {        int s = sum(root);        return ans;    }};