Groupon had a two round interview process. The first round was two back-to-back 45 minute on campus interviews. One was a design question and one was an algorithms question. They were pretty enjoyable. One of my interviewers had actually read my resume indepth, and checked out my github and asked me some pretty interesting questions about projects and some things I could have considered. The second round was three hour-long back-to-back Skype interviews. These were definitely more challenging, but otherwise decent. As a freshman, I didn't know enough to answer some of the conceptual questions, and struggled to implement some structures I was unfamiliar with, but overall the difficulty was alright. The algorithms questions were certainly very solvable.