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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.
Description seems to be already fixed (empty arrays)
It depends. If you assume an empty input to be a valid use case, then returning a string in this case it consistent with returning strings in the other cases (that rerurn binary numbers represented as strings".
It wanted a string of "0" when there is no sum. Shouldn't be an Integer?