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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.
This is definitely good enough for this case. If we had many more vowels, the search would end up being pretty inefficient, we should use a Set instead or anything with O(1) lookups.
Indeed, it seems to me this will redo
xs.counton each element, giving O(n^2) here. Would be careful where to use this.