The standard practice is for the interviewer to explicitly ask the candidate whether or not they have seen the question before. More frequently than one would

The standard practice is for the interviewer to explicitly ask the candidate whether or not they have seen the question before. More frequently than one would expect, the candidate will deny having seen the question before, zip through the solution, and then completely stall-out when they are asked to revise their solution to accommodate a very small alteration is made to the problem parameters.