Important Notice:

Practice-It will be discontinued as of November 1st, 2024. After this date, the website will remain online for a transitional period, but login will be restricted to University of Washington NetID authentication. This marks the next phase towards the platform's full retirement. Thank you for your use and support of the application over the years.

If you are looking for an alternative, a similar tool, CodeStepByStep, was developed independently by the original author of Practice-It, and is available at codestepbystep.com**

logo Practice-It logo

Main Page → Problems → Solve a Problem

writeNumbers

Language/Type: Java recursion recursive programming
Author: Stuart Reges (on 2014/02/13)

Write a recursive method called writeNumbers that takes an integer n as a parameter and that writes the first n numbers separated by commas with the odd numbers in descending order followed by the even numbers in ascending order. For example, the call: 

    writeNumbers(5);

should produce the following output: 

    5, 3, 1, 2, 4

The odd numbers (5, 3, and 1) appear first in descending order followed by the even numbers (2 and 4) in ascending order. Notice that commas are used to separate consecutive values in the list. Your method should send its output to System.out and should not call println. For example, the following calls: 

    writeNumbers(5);
    System.out.println();  // to complete the line of output
    writeNumbers(1);
    System.out.println();  // to complete the line of output
    writeNumbers(8);
    System.out.println();  // to complete the line of output

should produce exactly three lines of output: 

    5, 3, 1, 2, 4
    1
    7, 5, 3, 1, 2, 4, 6, 8

You must exactly reproduce the format of these examples. Your method should throw an IllegalArgumentException if passed a value less than 1. You are not allowed to construct any structured objects (no array, ArrayList, String, StringBuilder, etc) and you may not use a while loop, for loop, or do/while loop to solve this problem; you must use recursion.

Type your solution here:


This is a method problem. Write a Java method as described. Do not write a complete program or class; just the method(s) above.

You must log in before you can solve this problem.


Log In

If you do not understand how to solve a problem or why your solution doesn't work, please contact your TA or instructor.
If something seems wrong with the site (errors, slow performance, incorrect problems/tests, etc.), please

Is there a problem? Contact a site administrator.