Earlier quoted context omitted.
It depends how your interviewer is ranking/scoring you. One interviewer might be impressed with your ability to talk through and solve the problem from first principles, where another might ding you for not instantly knowing the answer. The former type of interviewer would be happy to give you hints and prompts, the second is a stone wall. I try to be the first -- it helps assess how a candidate responds to coaching…
> where another might ding you for not instantly knowing the answer While there certainly are incompetent interviewers, I think ones that extreme are rare.
See also: overused brainteasers. I remember being asked the 5 litre / 3 litre / get 4 litres problem for my Microsoft intern interview, and honestly told them that I already knew the answer, so I wouldn't be "solving" it, but here it is anyway...