Question

Consider the recursive function pingPong described below.

static String pingPong(int x) {
  if (x % 2 == 0 && x % 3 == 0)
    return "ping-pong";
  else if (x % 2 == 0)
    return "ping," + pingPong(x - 1);
  else if (x % 3 == 0)
    return "pong," + pingPong(x - 1);
  else
    return "?," + pingPong(x - 1);
}

a) what's the base-case of pingPong?

b) what's the result of pingPong(10)?

Answer 1

a) what's the base-case of pingPong?

In the given function, the base case is:

  if (x % 2 == 0 && x % 3 == 0)
    return "ping-pong";

It is called the base case because it terminates the recursion by not making any further recursive calls and provides a suitable output.

b) what's the result of pingPong(10)?

The output of pingPong(10) will be:

ping,pong,ping,?,ping-pong

The code with corresponding output is as follows:

import java.util.*;
public class ping{
    public static String pingPong(int x) {
          if (x % 2 == 0 && x % 3 == 0)
                return "ping-pong";
          else if (x % 2 == 0)
                return "ping," + pingPong(x - 1);
          else if (x % 3 == 0)
                return "pong," + pingPong(x - 1);
          else
                return "?," + pingPong(x - 1);
}

     public static void main(String []args){
        String s;
                s=pingPong(10);
                System.out.println(s);
     }
}

Output: