HR doesn't seem to understand the job description very well and called 100 people for Face to face discussion with 2-3 panels only. Due to which there was a long waiting hours before the beginning of interview. On top of that you were told by the interviewer that this is a drive for R&D department not for services which was nowhere related to JD shared in mail. Clearly if you are not prepared well with all Data Structures and Algorithm you'll not be able to clear the round. Still later HR will tell you that you have cleared the first round and will have Skype discussion for second round, which is a white lie and a childish way to ask candidates to leave and never hear from them again. Cause lets be clear about one thing that we being told that first round is not cleared is not going to kill us specially when we were the one who got interviewed and we know how it went. Suggestion to candidates appearing for interview in future to be sure about the JD given by HR. Clearly they mix up things and doesn't seem to care much. And this will lead you ending up wasting time or an opportunity if missing other interview for this one. Just cross check everything from your end.