Three phone calls. First one is going through resume. Second one is purely math, the third one is data structure related. The whole process is extremely mechanical, as if I was talking to machines, barely any interaction with interviewees. Each interviewer asked me to introduce myself, but there was no follow-up questions or discussion at all. The interviewers just pulled several brain teasers, math, or data structure questions from the pool and see if I can answer. There was a tech question that only takes me a few seconds to solve, but the interviewer suspected that I have done the same test before, and doubted my integrity and capability. I never fully understand what the interviewers are trying to do.