I was able to whiteboard an LRU cache implementation using hashtable and DLL. However the interviewer was arrogant and kept saying "this wouldn't work". When I explained with an example, he said "its not thread safe" and kept going into tangential topics. We ended with CAP theorem and options to make it thread safe. He made statements like "you never prepared for this interview, did you?" and "you guys are never ready for a good interview" when I turned back from the whiteboard. Overall very bad experience interviewing here, I highly recommend you not to answer recruiter calls from this company. They are unprofessional and arrogant.