Algorithm questions are not about the interviewer discovering what algos you know off the top of your head, but rather discovering how you solve a problem.

If the interviewer asks you an algo you know, and you bash it out super-quick, a prepared interviewer will just find another you _don't_ know the answer to. This thread's question is therefore somewhat missing the point.

Interview tests and questions which it's possible to swot up on aren't valuable. They only test your memory not your problem solving.