Add Digits(Easy)

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?

Java代码

public int addDigits(int num) {
    //For number that from 0 to 9, the answer is themselves
    //For number that is divisible by 9, the answer is 9
    //Otherwise, the answer is the reminder after divided by 9
    return num>9?(num%9==0?9:num%9):num;
}