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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 kata has a worst case complexity of O(n^2) and therefore a timeout is expected for longer lists. The use of memoization to avoid timeout is simply due to careful selection of test cases and as such, is not a critical component to the algorithm. I would recommend either removing long list test cases or emphasizing the use of memoization in the wording of the question.