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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
That's not the "official" documentation, but just a simple page of the Haskell wiki. The wiki provides many solutions to many problem sites out there, even to Project Euler. Also, nothing hinders one from posting the problem on StackOverflow.
IMHO this is a 6kyu or 7kyu kata, so it probably exists somewhere and has a solution ;).