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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.
Just because it takes 2ms on your computer doesn't necessarily mean anything. On most online judges, the constraints are large enough to tell you if your solution is unoptimized or not.