A recruiter emailed me and then scheduled a brief preliminary phone call. They asked about my experience and why I'd be interested in working at Facebook, and explained the recruitment process.

The next day, I was sent a front-end coding puzzle/challenge to complete, which took about 10 hours. Given a set of boxes with fixed vertical dimensions, I had to implement a JavaScript algorithm that laid them out according to some specifications.

A phone interview was scheduled about a week after completing the puzzle. I spoke with a front-end engineer and coded through a few HTML/CSS/JS questions using a shared document. My thought process was emphasized more than getting syntactically-correct answers, as long as I could explain what I was trying to do.

The next day, I was told I would move on to the next phase and was flown to California about 2 weeks later. The in-person interview consisted of 4 45-minute interviews, each of which was similar to the phone interview. We talked a bit about why I would like to work at Facebook and wrote code on a whiteboard. I was asked to write how I would implement visual UI features, array search/mutation algorithms, and JS performance functions.

Throughout the process, the recruiters were quick to reply to my emails and open to any questions I had. However, after I was told I didn't get an offer, they stopped being that helpful and couldn't offer me a way to obtain feedback about my interviews.

Given an input array and another array that describes a new index for each element, mutate the input array so that each element ends up in its new index. Discuss the runtime of the algorithm and how you can be sure there won't be any infinite loops.