Joachim Breitner

Fifth place in Godingame World Cup

Published 2015-04-26 in sections English, Haskell.

Last evening, Codingame held a “Programming World Cup” titled “There is no Spoon”. The format is that within four hours, you get to write a program that solves a given task. Submissions are first rated by completeness (there are 13 test inputs that you can check your code again, and further hidden tests that will only be checked after submission) and then by time of submission. You can only submit your code once.

What I like about Codingame is that they support a great number of programming languages in their Web-“IDE”, including Haskell. I had nothing better to do yesterday, so I joined. I was aiming for a good position in the Haskell-specific ranking.

After nearly two hours my code completed all the visible test cases and I submitted. I figured that this was a reasonable time to do so, as it was half-time and there are supposed to be two challenges. I turned out that the first, quite small task, which felt like a warm-up or qualification puzzle, was the first of those two, and that therefore I was done, and indeed the 5th fastest to complete a 100% solution! With only less than 5 minutes difference to the 3rd, money-winning place – if I had known I had such a chance, I had started on time...

Having submitted the highest ranked Haskell code, I will get a T-Shirt. I also defended Haskell’s reputation as an efficient programming language, ranked third in the contest, after C++ (rank 1) and Java (rank 2), but before PHP (9), C# (10) and Python (11), listing only those that had a 100% solution.

The task, solving a Bridges puzzle, did not feel like a great fit for Haskell at first. I was juggling Data.Maps around where otherwise I’d simple attach attributes to object, and a recursive function simulated nothing but a plain loop. But it played off the moment I had to implement guessing parts of the solution, trying what happens and backtracking when it did not work: With all state in parameters and pure code it was very simple to get a complete solution.

My code is of course not very polished, and having the main loop live in the IO monad just to be able to print diagnostic commands is a bit ugly.

The next, Lord of the Ring-themed world cup will be on June 27th. Maybe we will see more than 18 Haskell entries then?


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