They are quite clear that you can use the language you want (preferred = Java). For a candidate with 5 years experience, if I was the interviewer, I would expe

They are quite clear that you can use the language you want (preferred = Java). For a candidate with 5 years experience, if I was the interviewer, I would expect you to plow through this problem with ease, even on an awful whiteboard. The reason is that pub/sub is one of the systems that are quite important to know and understand for non-trivial enterprise applications. If you understand it well, you should have no problem in implementing a basic solution within an hour. I'm a big proponent of the idea that one shouldn't have to prepare for an interview beyond the curiosity of what the potential future employer do and which technologies do they use. Maybe you're really good at what you do and the question asked is too different from the kind of problems that you've been working on in the past few years. Are you good ? I don't know. I don't know you. Moreover, failing one interview does not answer that question for you. Neither is failing at 2 to N interviews...