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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 understood it like i had to sum it but ignore any duplicates of a value that we had already seen, not ignore both of them.
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I don't know if im just silly, but doesn'y it say we should sum the list but ignore duplicate numbers? If so how does [1, 1, 2, 3] not equal 6, but 5 instead?