Contents

RPCFN: Ruby**Fun 4

²⁶/Nov 2009 By Satish Talim

beginners rpcfn ruby

Ruby Programming Challenge For Newbies

RPCFN: Ruby**Fun (#4)

By Michael Kohl

About Michael Kohl

Michael Kohl (Twitter / blog) in his day job, works as an IT systems engineer in Vienna, Austria. He fell in love with Ruby in 2003 or so, maintained various Ruby-related packages for Gentoo Linux from 2004-2006 and started being an assistant teacher for RubyLearning.org in early 2009. Besides all things Ruby his interests include mathematics, literature, travelling, foreign languages, (functional) programming languages (e.g. Clojure, Haskell), chess and so much more that he really wishes he wouldn’t need to sleep.

Michael has this to say about the challenge:

The best way to learn programming is to write code! Ruby is fun because it’s easy to achieve results and I really believe that the RPCFN shows new Rubyists how much they can accomplish with relatively little Ruby. Thinking about a problem and then being able to compare your own solution to dozens of others is a lot of fun and a great opportunity for learning, so make sure to take part in these challenges! The reason that I picked this particular challenge is that it’s easy to solve, but requires a bit of thinking to get a somewhat attractive solution.

Prizes

The person with the best Ruby solution (if there is a tie between answers, then the one who posted first will be the winner) will be awarded any one of O’Reilly Media’s Ebook bundle.
The person with the second best Ruby solution (if there is a tie between answers, then the one who posted first will be the winner) will be awarded any one of PeepCode’s Ruby on Rails screencasts.
The other two prizes, selected randomly amongst the remaining working Ruby solutions, would be any one of:
- BDDCasts’ screencasts and any one of,
- Pragmatic’s The Ruby Object Model and Metaprogramming screencasts.

The four persons who win, can’t win again in the next immediate challenge but can still participate.

The Ruby Challenge

RPCFN

You just started working for CoolNewCompany which is developing mathematics related software. Since you are new to the team, your boss gives you an easy task to test your abilities. Write a class that pretty-prints polynomials, following some simple rules:

if a coefficient is 1, it doesn’t get printed
if a coefficient is negative, you have to display something like “- 2x\^3″, not “+ -2x\^3″
if a coefficient is 0, nothing gets added to the output
for x\^1 the \^1 part gets omitted
x\^0 == 1, so we don’t need to display it

Here’s a couple of usage examples:

puts Polynomial.new([-3,-4,1,0,6]) # => -3x^4-4x^3+x^2+6
puts Polynomial.new([1,0,2]) # => x^2+2

Don’t concern yourself too much with error handling, but if somebody tries to create a polynomial with less than 2 elements, your program has to raise an ArgumentError with the message “Need at least 2 coefficients.”

Please check the provided unit tests for more examples and make sure to use them for verifying your solution!

Requirements: This has to be a pure Ruby script, using only the Ruby Standard Libraries (meaning, no external Gems). You do not need to build a gem for this. Pure Ruby code is all that is needed.

How to Enter the Challenge

Read the Challenge Rules. By participating in this challenge, you agree to be bound by these Challenge Rules. It’s free and registration is optional. You can enter the challenge just by posting the following as a comment to this blog post:

Your name:
Country of Residence:
GIST URL of your Solution (i.e. Ruby code) with explanation and / or test cases:
Code works with Ruby 1.8 / 1.9 / Both:
Email address (will not be published):
Brief description of what you do (will not be published):

Note:

As soon as we receive your GIST URL, we will fork your submission. This means that your solution is frozen and accepted. Please be sure that is the solution you want, as it is now recorded in time and is the version that will be evaluated.
All solutions posted would be hidden to allow participants to come up with their own solutions.
You should post your entries before midnight of 20th Dec. 2009 (Indian Standard Time). No new solutions will be accepted from 21st Dec. onwards.
On 21st Dec. 2009 all the solutions will be thrown open for everyone to see and comment upon.
The winning entries will be announced on this blog before end of Dec. 2009. The winners will be sent their prizes by email.

More details on the RPCFN?

Please refer to the RPCFN FAQ for answers to the following questions:

Donations

RPCFN is entirely financed by RubyLearning and sometimes sponsors, so if you enjoy solving Ruby problems and would like to give something back by helping with the running costs then any donations are gratefully received.

Acknowledgements

Special thanks to:

Michael Kohl.
Sponsor Chargify.
Book Sponsor O’Reilly Media.
The RubyLearning team, namely Jeff Savin (Canada), Michael Kohl (Austria), Peter Crawford (Italy) and Satoshi Asakawa (Japan).

Questions?

Contact Satish Talim at satish [dot] talim [at] gmail.com OR if you have any doubts / questions about the challenge (the current problem statement), please post them as comments to this post and the author will reply asap.

The Participants

There are two categories of participants. Some are vying for the prizes and some are participating for the fun of it.

In the competition

Gimi Liang, China – declared winner (randomly selected)
William Yanez, Venezuela
Christiaan Van den Poel, Belgium
Tom Stuart, U.K.
José Sazo, Chile
James Daniels, USA
Pedro Diogo, Portugal
Felipe Elias Philipp, Brazil
Fabio Kreusch, Brazil
Milan Dobrota, Serbia
Jefferson Mariano de Souza, Brazil
Aldric Giacomoni, USA
Michael Lang, USA
Rohit Arondekar, India
Bill Sullivan, USA
Jorge Dias, Spain
Alexander Klink, Germany
Chris Jones, USA
Aurélien Bottazzini, France
Ali Al-Sahaf, Saudi Arabia – declared winner (randomly selected)
John McDonald, USA
Aleksey Gureiev, Ukraine – declared winner (best solution)
Fred Fordham, Australia
Tony Chen, USA
Rohit Sasikumar, India
Paul Harrington, USA
Aashish Kiran Chittimilla, India
Benoit Daloze, Belgium
Steve Wilhelm, USA
Marc Minneman, USA
Othmane Benkirane, Morocco
Oleksandr Manzyuk, Ukraine
Pankaj Sisodiya, India
Oliver, UK
Sérgio Silva, Portugal
Isley Aardvark, USA
Rémy Coutable, France
Brad O’Connor, Australia
Suraj Dhakankar, India
Sunny Dackie, India
Philippe Antras, France
Amr Tamimi, Palestine
Sriram Varahan, India – declared winner (second best solution)

Just for Fun

James Daniels, USA
Phil, Germany

The Winners

Winners

Congratulations to the winners of this Ruby Challenge. They are:

Aleksey Gureiev from Ukraine (his Ruby Challenge solution) – the person with the best Ruby solution. He wins any one of O’Reilly Media’s Ebook bundle.
Sriram Varahan from India (his Ruby Challenge solution) – the person with the second best Ruby solution. He wins any one of PeepCode’s Ruby on Rails screencasts.
Gimi Liang from China (his Ruby Challenge solution) – selected randomly amongst the remaining working Ruby solutions. He wins any one of BDDCasts’ screencasts.
Ali Al-Sahaf from Saudi Arabia (his Ruby Challenge solution) – selected randomly amongst the remaining working Ruby solutions. He wins any one of Pragmatic’s The Ruby Object Model and Metaprogramming screencasts.

Previous Challenge

RPCFN: Short Circuit (#3) by Gautam Rege.

Update

This challenge is now closed. Michael Kohl has a working solution to this problem. This is not a “perfect” or the sole “correct” solution, but just one way of doing it.
The (#5) challenge by Peter Cooper, UK is scheduled for 1st Jan. 2010.
The (#6) challenge by John Trupiano, USA is scheduled for 1st Feb. 2010.

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