Uniqueness of byte arrays
You need to read all items in the worst case. Assume you have written some algorithm which reads items in any order and processes them with any amount of cleverness. And I'm your opponent and try to make you read as many items as possible. 

Here's what I do: Whenever your algorithm reads an item I store an "X" just before you read it. I do that except when you have read one array completely, which consists of all X, and you are reading the last item of another array, in which case I store a value that makes this row different from all other rows that were read completely. When you read the very last item, I can decide to store a value that makes all arrays unique, or I store another X and you have two arrays that are identical. 

Whatever you do, until you read the very last item you don't know whether two arrays are identical or all arrays are unique.