Meta Onsite - BFS or DFS?

This might have changed but they had question banks you could work from but ultimately you would choose your questions as an interviewer. When the recruiters, hiring managers, directors, and sometimes the CTO! looked over the "packets" they would see how experienced the interviewer was and how often they used the question they asked and take that into account. So ultimately what Facebook strived for was FAIRNESS and CONSISTENCY. So the difficulty of the question wasn't as important as how well the interviewer was able to extract "signal" from using it. Some people had easier questions that they knew 100% strong no if the candidate didn't do well. Others had very medium questions that they expected to be solved perfectly and then had follow-ups they would use to build confidence that 1- person didn't memorize, 2- person really understood and could adapt on their feet to out of the box followups. You never know what you're going to get but the common trend is they want to see "clean code" and "clean solutions" - good variable names, clear logic, no extra ifs or loops, or duplicated lines of code that could be solved in fewer - more readable - lines, etc... If you overstudy and try to practice problems you'll get, you might pass through luck of the draw. If you focus on the meta (no pun intended) then you have a higher chance of passing on any question, even if your answer is not perfect. One of the best engineers I ever interviewed solved binary tree by level with new line in not the most efficient way, but crushed the meta.