563. Binary Tree Tilt

题目来源【Leetcode】

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

Note:
The sum of node values in any subtree won’t exceed the range of 32-bit integer.
All the tilt values won’t exceed the range of 32-bit integer.

这道题是求每个节点的左右子树的总值之差，也比较简单，直接放代码：

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ int f(TreeNode* root, int& sum){        if(root == NULL) return 0;        int l = f(root->left,sum);        int r = f(root->right,sum);        sum += abs(l - r);        return l + r + root->val;    }class Solution {public:    int findTilt(TreeNode* root) {        if(root == NULL) return 0;        int n = 0;        f(root, n);        return n;    }};