LeetCode: Add Digits

 1 public class Solution {
 2     public int addDigits(int num) {
 3         if (num < 10) 
 4         {
 5             return num;
 6         }
 7         int ans = 0;
 8         while (num > 0)
 9         {
10             ans += num % 10;
11             num /= 10;
12         }
13         return addDigits(ans);
14     }
15 }