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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.
I think this needs a very simple test example to illustrate what the requirement is, until that's in place I'm going to pass on this one.
Am I missing something on Codewars, why aren't these tests shown? This leads to a deeply frustrating experience as we have to guess what the test might actually be, just saying check your code is not acceptable.
Might be nicer returning an option from this (Java version).
I'm not sure how this ended up as the top solution, two passes over the collection is sub optimal.