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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.
Ah, thanks. (Sorry, I marked it as an issue before revising it after thinking I'd probably just missed something. Forgot to untag it)
This comment is hidden because it contains spoiler information about the solution
The description of the problem could be made clearer. I'm familiar with complementary DNA and I was still unsure. Here's a suggestion:
In DNA strings, the symbols "A" and "T" are complements of each other, as are "C" and "G". You are given a sequence and your function should return the complementary sequence. The sequence is given as a string (except for Haskell). For example, given the sequence string "ATTGC" your function should return the complementary sequence string "TAACG". The sequence you are given will never be empty.
Of course real-world requirements are often unclear so maybe it's just fine as it is :)