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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.
The last test with the very long array is confusing. Why should we get Log as a result? Gollum contains all the symbols l, o, g. So in this case we have no unique string?
Or please change the conditions from "contains unique or not contains some of repeating"
very short... and totally unclear
this is not about theory - it's about possibilities )
Maybe it makes sense to add test case with negative number?