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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 was actually able to pass the java test cases by only checking the rows.... Didn't even have to check columns or boxes.
One note that I would make is to add in the description the fact that there are no duplicate values in u. Took me a little while to get the correct answer as I did not know about this assumption and took me reading some of the discourse to figure that out.