leetcode

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?

class Solution {
public:
int addDigits(int num) {
int divideNum = 0;
if( num < 10)
{
return num;
}else
{
while( num )
{
divideNum += num % 10;
num = num / 10;
}
addDigits( divideNum );
}

}

};