Either 3 or 4 rounds of interview, depending on how you classify an interview because one was a bit short and ended up just talking about life. My first interview question was to give my best solution to a variant of the least common ancestor question. My next interviewer asked me about my experience and we ended up discussing some database join algorithms. I forgot the rest of the process but overall it was an amazing experience. I remember leaving feeling like all my questions were very challenging and interesting and that all of my interviewers were very warm, welcoming, and considerate. Groupon is definitely invested in their interns/employees.