[LeetCode] 258. 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.

Follow up:
Could you do it without any loop/recursion in O(1) runtime?

class Solution {

    public int addDigits(int num) {

        // 將num除以10 然後將所有餘數相加

        // 如果sum(餘數)除以10 ==0 return 餘數

        // num除以10 然後將所有餘數相加

         //!!不能用迴圈或遞迴

        

        int remind = 0;

        int temp = 0;

        while(num != 0){ 

            remind += num % 10;

            num /= 10;

               if(num==0 && remind>=10)

                {

                    num = remind;

                    remind = 0;  //忘記歸零，搞好久

                }

        }

                return remind;

      }

}