I was first sent a HackerRank challenge (one hour timed). It asked me to simulate a game, with rules explained, by reading inputs and determining the winner, loser, or tie. I passed 4/6 test cases.

The next two interviews were pair programming sessions on CoderPad and Skype. Both were one hour long, and the interviewers were interested not just in solving the problem, but in having me talk the whole time. I have the feeling they gave major bonus points for using object-oriented principles in my solution (they always started typing when I used inner classes), and they let me choose my language.

I was only asked about run-time once.

The final interview was on-site in San Francisco; they covered all transportation and food costs. I arrived with a group of six or seven other potential interns. The first hour or two consisted of a tour, a 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, which 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).

Imagine you have an x-y grid of floats.

Define a method to drop a parameter block of a certain height and length (also floats) beginning at any x coordinate.

Subsequent blocks dropped will fall on top of any previous blocks, 'stacking' their height.

Define another method to return the height at any requested x location.

There was a third method, but I didn't have time to do it.