I had my onsite for facebook recently. The first interview went well but the second was literally the worst interviewer I could have imagined.

Round 1:
I got two questions Simplify Path and Right/Left Side View of a Binary Tree. I got the first one in optimal time/space. The second one I had a little trouble in but I managed to solve it in 2 passes because I used the recursive solution instead of the BFS one by mistake. it was still in O(N) time just not as efficient.

Round 2:
I don't understand how this guy was allowed to be an interviewer. He only knew C++ and I was writing in Java. I got Pick Random index but instead of being passed an array I was told to make a function that added elements to a structure. I went with a List. I then had to spend the entire interview explaining to him why I was using a List instead of an array. By the time I had convinced him, I had 5 minutes left in the interview leaving no time for questions at the end. I did my best to code it up, but given how little time I had left there were probably mistakes and I didn't have the time to dry run.

Overall, that was the worst interview experiience I've ever had. Do better Facebook.