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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.
I don't like the fact that you call the lengths many times instead of having them in a variable
I don't like the fact that this solution modifies the arguments passed. Perhaps it would be better to use a shallow/deep copy?