Add Digits

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

Example

Given num = 38.
The process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return 2.

也可数学直接求解 https://en.wikipedia.org/wiki/Digital_root

public class Solution {
    /**
     * @param num a non-negative integer
     * @return one digit
     */
    public int addDigits(int num) {
        // Write your code here
        while(num>=10){
            int tempSum = 0;
            int temp = num;
            while(temp>=10){
                tempSum += temp%10;
                temp/=10;
            }
            num = temp+tempSum;
        }
        return num;
    }
}