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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.
that means your code needs to be more efficient, try to optimize your code more:)
You're right, the problem only specifies "letters," which is open to interpretation. My solution passes all tests, so perhaps the author did not have foreign letters in mind.