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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.
In Haskell, this should probably use Nothing rather than -1 as a sentinel value.
The problem statement should say "letters", not "alphabets". The alphabet is the set of all letters, not a word for individual letters.
Haskell version won't even compile; the module naming seems to be different from what the environment expects.
I believe it means the previous kata in the series. This is part 3 of a 3 part series.
The problem statement refers to "the previous kata", but katas do not necessarily get presented in any particular order. Perhaps a link to the kata referred to would be better.