I think the author prefers people to find out how to handle duplicates by reading the discourse section, since the vague note in the instructions, "(with <)" has been unchanged despite all the suggestions to clarify it.

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.