Meta Software Engineer interview questions

I was contacted by a Facebook recruiter via LinkedIn and within a few days had non-technical 30 minute phone interview, after which we scheduled a first technical interview that could be done in person or over the phone. Since I live in the area I opted to do it in person at the Menlo Park facility. The recruiter supplied me with links to several sources of preparation materials, and asked for dates which I might be ready for my first technical interview. I opted for a date two weeks from the phone screening. On the day of the interview I was greeted at Facebook by the recruiter, who showed me around the campus, which consists of 16+ buildings and has lots of amenities. The recruiter brought me to a small meeting room with two whiteboards and a few minutes later the interviewer showed up, accompanied by an observer. The first thing they did was ask me about any current projects I'm working on, and about the tech stack I use. After talking about that for a few minutes they presented me with a coding problem, which I could do in a language of my choice. I have not done many of the typical coding challenge problems you might see on LeetCode or similar sites. I was relying on experience and my ability to work through a problem. I read somewhere that interviewers care more about how you approach a problem than how well you can churn out memorized material, so I thought I'd be better off focusing on my overall approach and communication skills. In that regard I think I did well but after reading some other reviews, perhaps I worked too slowly and could have benefitted from doing more of those more academic coding exercises. I was given one problem and took the whole 45ish minutes to do it. I started with a very general conceptual solution done visually, and then wrote it up as executable code, while addressing bug and ways it could be made more efficient. Afterwards I was asked to execute the solution on the whiteboard as if I were an interpreter running the code, noting intermediate values and output. I did not find the problem very difficult but I wanted to make sure I stayed engaged with the interviewer and talk out the solution while working on it, which is not how I typically code on my own.

I applied through employee referral in September, passed the phone interview for easy programming questions and explanations. The onsite interview was three rounds with one interviewer in each round. After two days I was rejected.