Meta Machine Learning Engineer interview questions

It was a 5 round interviews. 2 rounds are technical, 1 round system design, 1 round theoretical interview, 1 round behavior. One technical question is tedious. The idea is not hard but the implementation needs a lot of tricks. The interviewer was not friendly. I felt like herself even didn't know the best approach. The system round was standard, but apparently the interview didn't like to think outside of box. He only wanted to hear standard answer. The theoretical round is ridiculous. I expected a deep and math-oriented discussion, but the interview only asked me to state my knowledge on RNN and CNN, which has nothing to do with any math at all... I didn't learn anything new in the interview. Very disappointing.