// Class countdown will countdown from any positive number down to zero
public class Countdown {
   
   public static void main(String[] args) {
      countdown(5);
   }
   
   // recursion: a method calling itself
   // Think about what happens when n is negative?
   // How should we address this case?
   public static void countdown(int n) {
      if(n == 0) {
         // base case
         // the problem is so small we just do it
         System.out.println("0!");
      } else {
         // recursive case
         // - doing a little bit of the work
         System.out.print(n + " ");
         // - solving a smaller problem by recurring
         countdown(n - 1);
      }
   }
   
   public static void countdownFrom3() {
      System.out.print("3 ");
      countdownFrom2();
   }
   
   public static void countdownFrom2() {
      System.out.print("2 ");
      countdownFrom1();
   }
   
   public static void countdownFrom1() {
      System.out.print("1 ");
      countdownFrom0();
   }
   
   public static void countdownFrom0() {
      System.out.println("0!");
   }
   
}