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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.
Few suggestions to the author:
Fix task description - very vague explanations that mislead.
Test cases don't show the problem in your code, generally, they always pass, and only after an attempt I can see some errors.
The difficulty seems to me rather 6 kyu.