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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.
Good!
I came up with the same solution, thought I was doing some horrible hack xD
I believe you'd do better in terms of time efficiency if you used a set to check which elements have already been added: checking membership of a list is a linear-time operation, but for a set it's pretty much constant (neglecting collisions).
But this is better in terms of memory efficiency, so I guess there are pros and cons.