The interview process was very informal, despite a few questions read from a very HR-sounding document.

I met with three people. I wore a suit, but now I know that was definitely not required, given the laid-back, startup-like atmosphere.

I had two or three phone screenings prior to the in-person interviews.

There are 100 people standing near the beginning of a row of 100 closed doors.

The first person goes down the row and opens every door.

The second person closes every 2nd door.

The third person changes the state of every 3rd door, and so on.

Write a routine to find the state of door X after person Y passes by.