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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 faced same situation, look for test cases in Ruby version, it will be all clear why it failing
Brute force is not the "correct" way.
Use mathematical formula, N/2(A+L) = N/2(1+N) = (n/2)*(n+1)
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