I was first sent a HackerRank challenge (one hour timed); all it wanted was to simulate a game (rules were explained) by reading inputs and determining who won, who lost, or if there was a tie. Passed 4/6 test cases. The next two interviews were pair programming on coderpad and Skype. Both were one hour long, and the interviewers were interested in not just solving the problem, but in having you talk the whole time. I have the feeling they gave major bonus points for using object-oriented principles in your solution (they always started typing when I used inner classes), and they let you choose your language. I was only asked about run-time once. The final interview was on-site in San Francisco, they covered all transportation/food costs. I came in with a group of six or seven other potential interns, and the first hour or two was a tour, history of Square, and lunch. Then they led us to a set of open desks where we had our last two technical interviews back-to-back (each one hour long -- I spaced out on the last one, that disqualified me). After that we had coffee, a sit-down chat with some engineers, and then a send-off with swag. Overall, it's been my favorite interviewing experience (no whiteboards at all, just coding and chatting).