It is strongly advised that if you get a question you've already practiced then you should tell your interviewers. At least that's the supposed code of conduct. So, what you're suggesting is that the code of conduct is just words and this is all just a set of moves that we have to go through.
What code of conduct? Who advises that? Expecting that to be followed seems like it would just disadvantage honest hard studiers and honest people who actually do figure out the solution on the spot, while rewarding dishonest talented performers who also happen to be hard studiers—so unless that's what you're trying to select for....
