Meta Software Developer interview questions

After successful skype interview I came onsite. There were 4 stages, warmup session, 2 explicit coding sessions and one design session. I was overstressed and terribly performed during warmup session, next 2 were normal and the last was ok. Interviewers were friendly enough, they tried their best to help me overcome my stress.

The recruiter was nice and all the interviewers are friendly. I solved all the questions but still fail the interview, I think they really need totally bug free!!!! It is said interviewer will run the code from white board!