I got 3-rounds phone-screen and 1 round on-site interview. In the first round phone-screen, the interviewer asked me some general questions about my research interest and my current project. He also introduced some details about their group. In the second round, the interviewer asked me how to solve a problem they encountered currently. He gave me just brief information and asked for basic idea. He also asked me a very basic programming question. If you have solved all problems on leetcode, you can surely handle that. The interviewer for the third round didn't show up. The on-site is amazing. Facebook pay for all the expense. The hotel is great and I even rented a car. Three researchers interviewed me for some research questions. How to solve the practical problems. And one interviewer asked me to explain the idea of a programming problem and write some code on white board. I found it hard to explain algorithm without any code.

2 Technical Interviews. First was a relatively standard coding interview, except the coding question was very difficult. Second was more along the lines of my work, so I guess its a technical review of how indepth you know your stuff.