Leetcode258-addDigits

Description

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?

Solution

class Solution {
    public int addDigits(int num) {
        while (num >= 10){
            int temp = 0;
            while (num / 10 > 0){
                temp += num%10;
                num /= 10;
            }
            num += temp;
        }
        return num;
        
        //Follow up:
        //return num == 0 ? 0 : (num % 9 == 0 ? 9 : (num % 9));
    }
}

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