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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.
IMHO This is readable but bad performance wise.
IndexOf & lastIndexOf iterate over all elements in the array. Therefore, this will have a quadratic time look-up since the function is looking at a every index in the array 3 times.
Tests seem to be broken.
I keep getting expected [ undefined ] to deeply equal [ 1, 2, 3, 7, 16, 17 ] even though I am returning the array in the correct order