#Leetcode# 258. Add Digits

https://leetcode.com/problems/add-digits/

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

Example:

Input: 38
Output: 2 
Explanation: The process is like: 3 + 8 = 11, 1 + 1 = 2. 
             Since 2 has only one digit, return it.

代码：

class Solution {
public:
    int addDigits(int num) {
        return (num == 0) ? 0 : (num - 1) % 9 + 1;
    }
};

　　求数根 原来是有规律的 对 9 取余