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javarecursionmethodsprinting
Ulvi Bajarani
Ulvi Bajarani

Reputation: 13

Printing integers in the ascending order recursively

Today, I have taken an exam, and there was a question:

Write a method which prints integer numbers in the ascending order recursively from 1 to n:

public class PrintIntegersAscendingOrder {

    static int counter = 0;
    public static void PrintIntegersAscendingOrder (int n)
    {
        if (n == 1)
        {

            System.out.printf("%d\n", ++counter);
        }
        else
        {
            System.out.printf("%d ", ++counter);
            PrintIntegersAscendingOrder(n-1);
        }

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

Although this method worked now, the initial question didn't ask for the class definition, but the method. There, I couldn't be able to fit counter (I have written counter inside the if on the paper, but it gives an error in the program). How can I write the method precisely and correctly without counter variable?

Upvotes: 0

Views: 2289

Answers (3)

dariosicily
dariosicily

Reputation: 4517

In your code you have defined in your class a method PrintIntegersAscendingOrder having the same name of the class PrintIntegersAscendingOrder containing it. This is an error that can be avoided for example renaming the including class to PrintIntegers. Below the code of class without the error and with the recursive method: 

public class PrintIntegers {
    public static void PrintIntegersAscendingOrder(int n) {
        if (n > 0) {
            PrintIntegersAscendingOrder(n - 1);
            System.out.printf("%d\n", n);   
        }
    }
    public static void main (String args[]) {
        PrintIntegersAscendingOrder(5);
    }
}

Upvotes: 0

Arvind Kumar Avinash
Arvind Kumar Avinash

Reputation: 78945

Do it as follows:

public class Main {
    public static void printIntegersAscendingOrder(int n) {
        if (n == 0) {
            return;
        }
        printIntegersAscendingOrder(n - 1);
        System.out.printf("%d ", n);
    }

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

Output:

1 2 3 4 5

As @RobOhRob has already pointed out, the counter defeats the purpose of recursion in your code. When you are calling a function recursively, you need to analyse three important things:

  1. When to stop the recursive call
  2. Processing before making the recursive call
  3. Processing before making the recursive call

Since you are already decreasing the parameter by 1 and passing it to the method to call it recursively, you can simply make use of this parameter instead of creating an additional variable (e.g. counter).

Upvotes: 1

Swapnil Ingle
Swapnil Ingle

Reputation: 128

You can do it like this:

public class IntegerAscendingOrder {
    public static void main(String[] args) throws Exception {
        printIntegersAscendingOrder(n);
    }

    private static void printIntegersAscendingOrder(int i) {
        if (i < 1) {
            return;
        }

        printIntegersAscendingOrder(i-1);
        System.out.println(i);
    }
}

You don't need the counter variable in the class, using recursion you can limit the method call within the method itself.

Notice the if (i < 1) {return;} line, this will terminate the recursive method call(s).

This article should help you Getting started with recursion

Upvotes: 3

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