Question:

Write a recursive method called countDown that takes an integer n as a parameter and prints the numbers from n down to 1, separated by commas. For example, if n is 5, the method should print "5, 4, 3, 2, 1". Your method should stop when it reaches 1. Assume that n is a positive integer.

Write the countDown method using recursion and demonstrate its usage by calling it from the main method with an input of your choice.

Answer:

public class RecursiveCountdown {
    public static void countDown(int n) {
        if (n == 1) {
            System.out.print("1");
        } else {
            System.out.print(n + ", ");
            countDown(n-1);
        }
    }

    public static void main(String[] args) {
        countDown(5);
    }
}

Explanation:

In the given solution, we have a recursive method called countDown that takes an integer n as a parameter.

• If n is equal to 1, our base case is reached, and we simply print "1".
• Otherwise, for any other positive integer n, we print n followed by a comma and space. Then we make a recursive call to countDown with the updated parameter n-1.

In the main method, we demonstrate the usage of the countDown method by calling it with an input of 5. This will result in the output "5, 4, 3, 2, 1".