Comment by photon_lines

Yeah - I was going to say the same thing. Hashing would be the way to go if you're going for runtime and efficiency. You select the elements in an ordered manner though so that makes it n*log(n) and then produce a hash value for each table (or each row in the table) -- I'm trying to think if there is a better way of doing it in less time right now but I'm not seeing it yet. You could do this in O(n) or even constant time but it adds a bit of complexity to the solution I think.