For background, I work currently at one of the FAANMGs and I have spent around 20 years in the industry. I actively interview candidates and I have had offers from 4 of the FAANMGs not too long ago. My experience is that the preparation required varies. It depends whether you are interviewing as a general SWE or pre-slotted. If you are pre-slotted, one or more interviews tend to be specific to your domain and skills. You do need to know Big-Oh notation, trees, BFS/DFS and such standard stuff at most of the places; but how much the interviewer go to basic CS theory tend to vary based on your domain and years of experience.

For example, as an interviewer I often ask computer architecture/operating system questions as that’s what someone coming in, slotted into my team, needs.

In general, a lot of coding questions tend to be pattern matching and how fast you recognize the algorithm/data structure required to solve it. Before going in as a candidate, I did 50-60 leetcode puzzles and a bit of Elements of Programming Interviews. I also interviewed at many places for FAANMG readiness.

All said and done, the biggest factor in interviews is luck - from getting a good interviewer to getting a problem that you can easily identify/enjoy solving. All the preparation stuff is just to hone your skills. More you’ve seen going in, the better.

Best of luck!