This was for a position in their Infrastructure team in Cambridge, MA.

Recruiters contacted me in September and were very interested in my background and experience with highly scalable systems, both in Finance and Mobile phone payments.

I attended some small, intimate presentations they held as they were initially opening a new Boston office and wanted to grow it out. The meetings were great, and I learned a lot about how they solve some of their biggest problems.

I then did a screening interview on-site (because I don't do technical screens well on the phone). The question was: "Given a binary tree, write code to print the tree out line by line." I did okay and got the Breadth-First Search down fine, but couldn't figure out the line-by-line part. (Turns out this is Facebook's #1 question to ask in interviews).

Although my performance wasn't great, they gave me a break on that and asked me back for another screening interview. This time, I prepared well for another coding interview, but it turned out to be a Design interview. The problem was:

"Imagine you have 10,000 servers and need to monitor the performance of each one; how would you do it?" Naturally, you need to be able to not take too much bandwidth, so you'll have to do sampling, have some history to watch for trends, etc.

I passed that and was very excited to be flown out to Menlo Park for the final round.

I studied like crazy based on questions on this site and CareerCup. I took 4 weeks and studied about 15 hours per week.

It turns out I focused on the wrong questions. I studied Tree, String, Array, and List algorithms based on the distribution of Q&A, but I was asked Binary math and heap algorithms. Here are the questions I was asked:

1. How would you implement division without +, -, or multiplication? (A "classic" question, but not one of the ones I would focus on.) I bombed on this as I was not expecting it and could not recall my binary math. I figured out the high-level outline, but that was all. That I was asked this in the "culture fit" interview made this doubly unexpected.

2. Given 10,000 servers containing a billion integers each, how would you find the median? I knew the answer to this question (use two heaps), not because I had focused on it, but I had found it an interesting question while studying. However, they then asked, "How much memory do you need?" and I didn't know how big the heaps would need to be. The real answer I was trying to get is: what is the minimum heap you need? I had a guess, but I think I got this wrong.

3. Given a List structure where each node contains a Next node and optionally a pointer to another list, flatten that list. e.g. L1 --> L2 --> L3 --> L7 --> L8 | v L4 --> L5 --> L6

   Will be flattened to: L1 --> L2 --> L3 --> L4 --> L5 --> L6 --> L7 --> L8

   I did okay on this, getting the answer, but it appeared I took too long. The interviewer also interrupted me a lot while I was writing an initial solution, and that threw me off. I like to be more iterative in my problem-solving, but I think he expected 100% immediate correctness. He had an observer there, too, and that guy looked bored out of his mind, and that bugged me a little, as it wasn't clear who would be doing the judging.

4. I was also handed some hard-to-read Python code (I don't know Python) and asked to figure out what it does. I did okay on this, but again, I was surprised to be handed hard-to-read code in a language I didn't know.

5. One final question: "How would you implement the 'ls' Unix function in your language of choice? It should take the input: ls a/b/c/*/e/*/f/*/*/g and the output should be similar to the output given by Unix."

I used a tree structure to represent the file directory structure and wrote a solution from there. I did okay on this.

Overall: Everyone seemed very nice. I had a nice lunch, and the campus is interesting, but it was clear that what I studied was not what I needed to (so, lesson learned: don't just trust the distribution of questions on Glassdoor or CareerCup). I even got to walk past Zuckerberg's office (more of a conference room) and saw Sheryl Sandberg in there.

One interesting thing I learned is that a lot of Google people are leaving for Facebook. Also, I'd say if you are over 30 (I am 41), you are a rare bird at Facebook :)

I knew based on the reactions of the interviewers that it was very probably a bust, but overall a good experience and something I will learn from. Very disappointing, as I really wanted to be one of the first few Facebook engineers in the Boston area and to work on their super high scalability issues, but such is life.

How would you implement division without +, -, or multiplication?