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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.
this would be mutation of inputs:
No, the problem stays the same, the strings could contain commas, what if one of the strings in a1 is something like "cd,ef" and a2 contains ["abcd", "efgh"], you would not want to return this "cd,ef" string from a1.
this one is wrong in this case : {"a1": ["abc", "def"], "a2": ["abcd", "ef"]}