[Leetcode]258. Add Digits

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

For example:

Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it.

Follow up:
Could you do it without any loop/recursion in O(1) runtime?

这个题目当时看了下，找找规律就写出来了。。。

class Solution {public:    int addDigits(int num) {        return 1+(num-1)%9;    }};