Everything seems normal at the beginning. I got referred from a friend to FB and got a phone screen pretty soon. The interviewer showed up 5 mins late and jump right into his 2 coding questions.

First questions is normal palindrome question: "How to check if a string is palindrome for 'a' to 'z', it may contains other letters like 'K' or '5' or '#' etc. " I basically worked it out in about 10 mins by using 2 pointers

Second question is to convert an input integer into a string in hex" i.e. 10 -> "A". I used a string builder and worked it out in about 10 mins again. But I made a mistake of appending each char at the end instead of at the front but I fixed it after test with a use case.
After that we chatted for about 20 mins about how the teams in FB work and various topics. I thought we had a pretty good conversation.

Here comes the weird part, after 2 days, the recuiter emailed me saying my coding part did not meet their expectation.
I was like what??? How come you questioned me with those straight forward questions and saying my code did not meet the expectation? I'm very disappointed by the interviewing process if this is the way they handle it. Anyway, just something to watch out guys.

Peace