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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.
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I definitely agree, since the instructions say "with the strings filtered out", not "with only the integers returned". The other solutions seem to just be passing the test cases, as opposed to fully following the instructions. Perhaps a random test with different data-types could be added?