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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 an interview they would ask you to do this in place.
Looks clever but in terms of cost:
you have to scan the string many, many times
each time you do parens.replace you are generating a new string.