【leetcode】【Easy】【258. Add Digits】【Math】

题目：https://leetcode.com/problems/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?

code:

public class Solution {
    public int addDigits(int num) {
        return (num-1)%9+1;  //0为特殊情况，不要忘记考虑特殊情况 
    }
}

答案有几种可能--->9种，1~9-->有没有数学规律？--->有，9个为一个循环

注：

(-1)%9=-1