leetcode-258. Add Digits

1、来源：点击打开链接

2、内容：

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?

3、代码：

class Solution {public:    int addDigits(int num) {        int i;        while(num>9){            num=num/10+num%10;        }        return num;    }};

4、参考点击打开链接：

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