As far as difficulty, the interview was pretty standard. Facebook has a very low tolerance for bugs/mistakes, so definitely test hard!

Having received offers from major companies (Google, Microsoft, and Amazon) and having 8+ years of experience at one of these, I feel reasonably confident in saying I wasn't challenged. Instead, the whole process felt like an exam, and most interviewers behaved like examiners, not collaborators.

There was very little discussion or debate. During four coding rounds, the interviewers took a backseat right after they gave me the problem statement. After I was done coding, the interviewers examined my code and stated their objections to it, such as:

• There's a wrong variable name that won't let your code compile.
• Please don't use your own utility functions; I've provided you with a few.
• Your code doesn't meet my contract exactly (I did implement an optimization, with the verbal agreement that the client didn't need the extra data).

In my system design round, I was asked to scale out a complicated data structure. I did make reasonable progress, but the interviewer and I were playing catch-up for the entire interview.

Two interviewers told me to implement a 'silly' protocol or a 'silly' class. This clearly makes it an exam, and not a true discussion/debate, since it is not possible to make many logical arguments.

I'm under NDA, but this is not very different from any other tech interview.