AddDigits.java

/* (C) 2024 YourCompanyName */
package math;

/**
 * Created by gouthamvidyapradhan on 02/08/2017. Given a non-negative integer num, repeatedly add
 * all its digits until the result has only one digit.
 *
 * <p>For example:
 *
 * <p>Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return
 * it.
 *
 * <p>Follow up: Could you do it without any loop/recursion in O(1) runtime?
 */
public class AddDigits {

  public static void main(String[] args) throws Exception {
    System.out.println(new AddDigits().addDigits(38));
  }

  public int addDigits(int num) {
    if (num == 0) return 0;
    return num % 9 == 0 ? 9 : num % 9;
  }
}