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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.
Now this is what I call a clever solution!
The author's description of the challenge contradicts the test cases. The test case includes the single quote marks when counting duplicates even though the description says the strings will only contain alphanumeric characters.