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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 top voted solution is not random.
Each row starts with
['A','B','C','D',...]
. I suggest adding a test like the one below, which catches the case where at least one column is all the same letter. This happens only 10 out of 4^9 = 262,144 times (0.004% odds) in a truly random array. So the vast majority of the random arrays should still pass with this new test in place.