From the many experiences that I have had attending and conducting interviews, less of the former and much more of the latter, I have come to realize that there is very rarely a correct answer to a question that the interviewer asks.
Interview questions, especially at the professional level (as compared to fresher level) can be quite interesting. Whereas in the fresher level, one usually blurts out answers by the book and there is no way to contradict what one says since that is how it is mentioned in the book. In the professional level, there is much less bookish theory involved. It is more about application and practicality. This is where the problem creeps in.
Even two colleagues working in the same company and on the same technologies cannot 100% satisfactorily answer another one’s question. Especially when you move out of the basic questions and start delving deep to gauge the knowledge of the other person. What you think should be the answer to a problem, really need not be the answer that the person has in mind. He may have an alternate individualist approach to the problem, but then you(as an interviewer, or interviewee) have tuned your mindset in a particular fashion and you expect the other party to answer you the way you want to hear it.
The correct answer to a question is always the one that the interviewer wants to hear.
There are no two ways about that. If I am asked to cross a river, I might want to do a backstroke, while the examiner wants to do it freestyle. Each of us have our own preferences and do things our way.
As an interviewer, what I usually do is to gauge the confidence with which the other person is giving his/her answers. I might not know the topic, but I try and probe into what the other person is saying to see if he/she has all his/her tracks covered. This gives me the best indication, not only of what the other person knows, but also how capable the person is when something new is in the offing.
As an interviewee, the best bet is to frame questions to understand what exactly the interviewer wants to hear. Take your time before you come up with an answer. I think it is better to be judged as an inquisitive candidate, than a wrong candidate for the job. It is also important to judge the interviewer. If you think you are right and the interviewer is not really convinced, then ask a question of the interviewer whether they are happy with your answer and/or would like you to try in a different way. Be 100% sure that the interviewer has not misinterpreted or misunderstood what you have said. After all, it is your job opportunity to loose.