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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.
The best solution here in terms of performance, only iterates onces over the list.
I don't like this solution, you put clarity before performance.
Your solution loops 3 times through the list when you can make in just once