Meta Developer interview questions

I was first called by a FB recruiter and we chatted about 15 min about my general background information. I then was followed up with a phone interview with a FB engineer. He seems to be an experienced engineer. He started with a common background question like challenge of current project. Then, he asked me to design the Facebook Credit system. I proceeded with talking about I would started with designing the backend of the system, for example a ER diagram that would outline the relationship between existing user information and the new information related to the FB Credit system. I was a little nervous at the beginning, but the interviewer jumped in and gave me some help. He then asked me how would the total credit points of a user be calculated based on my design. For that question, I answered how the data is delivered to user from end to end in a multi-tiered web application. Next is the programing question (write a function to convert an ASCII representation of a positive integer to it's numeric value). I had a subtle bug in my code, but in general I got it right. I coded in PHP, the interviewer is satisfied with it since FB uses lots of PHP. The last 5 min was for me to ask him some questions. The interviewer was very professional and helpful during the interview. He was able to follow my thoughts and provide hints.

First I had a phone interview. The question was fairly straight-forward (multiply two very large numbers given as Strings) and the interviewer wasn't looking for any tricks or anything like that to solve. Like others have mentioned, quick clean code seems to be the key. Unfortunately, the interviewer had a very thick East Asian accent and talking over the phone just made things worse. I had to ask him to repeat quite a few times. It was probably me but at times I couldn't even tell when he'd asked a question because of the inflection! It must've gone well enough though because I got an on-site call. The on-site was two interviews of 45 min each. In the first one, I took a bit of a hit because a) I couldn't see the solution right away b) it took me a while to get up to speed and code the thing - I did manage to finish it though and it seemed (relatively) bug-free. Again, as lots of people have mentioned, the interviewer seemed quite young, just a year or so out of school and he didn't offer much in terms of feedback - positive or negative - as the interview progressed. Once he'd given me the question and given me the hint that got me started, he was busy with his iPhone, rarely looking up. That kinda sucked. The second interviewer was much nicer - probably one of the best ones I've interviewed with - lots of feedback, lots of encouragement, was accepting of different trains of thought and non-standard answers. Seemed like a really nice guy too. Overall, it seems to be the case with Facebook that a) Your interview really depends on who you get b) They seem to value quick-clean-bug free-optimized code at the first try more than anything else c) Questions are of average to above-average difficulty (if you've prepared!)