I was contacted by a Facebook recruiter and decided to give it a try. I selected an in-person technical screen over a phone interview because I believe it's much easier to express oneself in person, especially with the advantage of a whiteboard. This is particularly helpful for graph or tree problems where drawing is essential.

Unfortunately, I had to sign an NDA, so I cannot share the exact questions. However, for a non-senior software engineer role, the question was quite challenging to solve within 40 minutes. It required backtracking, and the optimal solution involved n! (n factorial). If you haven't encountered this problem before, it's likely you would spend considerable time identifying the optimal solution before even starting to code, as I did. Nevertheless, I was able to code most of the solution, and the interviewer seemed happy, even stating so himself.

The interviewer was very pleasant, answered my questions thoroughly, and seemed down-to-earth. My only uncertainty lies in the choice of question. I was informed that they would not proceed with the on-site round, which is what I expected.

NDA signed.

The question involved matrix calculations and required backtracking. The best solution was n!.