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?

迭代比递归快。

代码;

class Solution {public:    int addDigits(int num) {       while(num>=10)       {           int temp=0;           while(num>=10)           {               temp+=num%10;               num=num/10;           }           temp+=num;           num=temp;       }       return num;    }};