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Facebook Software Engineer Interview Questions & Reviews

Updated Apr 17, 2014
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Software Engineer Interview

Software Engineer
London, England

I applied online and the process took 2 months - interviewed at Facebook.

Interview Details Initial phone conversation with facebook recruiter of about 20 mins, going over my background and experience as well as what I was looking for.
Set up a phone interview with a shared screen coding question, was suggested 2 weeks to prepare.
Had I passed this stage, would go into London for an all day interview.

Interview Questions

  • Find lowest common ancestor (LCA).   View Answer
  • Given two unsorted arrays, one with event start times and one with end times, find out if any two events overlap.   View Answers (3)
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Software Engineer Interview

Software Engineer
London, England

I applied through an employee referral and the process took 7+ weeks - interviewed at Facebook.

Interview Details They were as friendly as you can imagine and gave me a T-Shirt. I met a kind of famous security guru.

Interview Question – How do you print all elements of a linked list.   View Answer

Reason for Declining – I'm still in the loop.

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1 person found this helpful

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Software Engineer Interview

Software Engineer
London, England

I applied through a recruiter and the process took 4+ weeks - interviewed at Facebook in January 2013.

Interview Details First interview: 20 minute phone conversation about past experience with a technical recruiter that works for them.

Second interview: 45 minute phone interview, with a PC in front. He gave me some details about the company and gave me one coding challenge.

Interview Question – During the second interview, I was asked to implement LCA in a binary tree (not BST) on collabedit.com. I was close, but not close enough...   View Answer

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41 people found this helpful

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Software Engineer Interview

Anonymous Interview Candidate
Menlo Park, CA (US)

I applied through a recruiter and the process took 3 months - interviewed at Facebook in November 2013.

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

Recruiter contacted me in September and was 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 did 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 OK 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 of the bandwidth and 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.

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 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 how to 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 he 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 OK 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 too 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 OK on this - but again 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 the the output given by unix."

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

Interview Question – How would you implement division without +, - or multiplication   View Answers (4)

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Software Engineer Interview

Anonymous Interview Candidate
Menlo Park, CA (US)

I applied through a recruiter and the process took 3 weeks - interviewed at Facebook in March 2014.

Interview Details I was contacted by a recruiter in early 2014. I was set up with an engineer for a phone interview. The first few questions were about my resume, simple stuff about projects I've worked on and prior experience. Then I was asked two technical questions, one about recursion and one about trees. I fully solved and optimized the tree problem but struggled a bit with the recursive problem. Overall it wasn't too difficult but make sure you prepare well before going in!

Interview Question – A recursive problem involving how many combinations you can make out of a set of numbers. Know your data structures, the problem used both hash tables and lists.   View Answer

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Software Engineer Interview

Anonymous Interview Candidate

I applied through college or university and the process took 2 weeks - interviewed at Facebook in February 2013.

Interview Details Quick hiring process - first interview is all technical. It will be all on algorithms and memory complexity.

Interview Question – I don't recall, was a while ago.   Answer Question

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Software Engineer Interview

Anonymous Interview Candidate

Interviewed at Facebook

Interview Details Recruiter contacted me from LinkedIn profile and got me first round of interviews in NYC office

Interview Question – How do you find the kth smallest number in a binary search tree.   Answer Question

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No Offer

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Software Engineer Interview

Anonymous Interview Candidate

I applied through an employee referral and the process took 1 week - interviewed at Facebook in January 2014.

Interview Details Phone interview and then on site. In the phone interview, they ask me to solve the 3 sum problem (check leetcode) and the bucket anagram problem. In the on site interview, 3 interviewers ask me three algorithm problems and also the behavior problems. Then there's a brief tour to the campus.

Interview Question – On site interview, they ask me regular expression match (check leetcode) and search for range (like, 1,2 3, 7,7,7, 9, 9, return how many 7's in the array) and also knowledge about the garbage collection, linked list, reverse linked list.   View Answer

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Software Engineer Interview

Anonymous Interview Candidate
Menlo Park, CA (US)

I applied through a recruiter and the process took 1 week - interviewed at Facebook in April 2012.

Interview Details They found me at SO careers for some reason. First we had a HR with nothing really particular then an other skype/phone interview with real time coding. The guy was ok and friendly, answering all my questions. It was the usual American style interview with absolutely meaningless basic CS questions.

Interview Question – Why do you want to work at facebook? (I didn't really... :))   Answer Question

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Software Engineer Interview

Anonymous Interview Candidate

I applied through a recruiter and the process took 3 weeks - interviewed at Facebook in March 2014.

Interview Details Phone call interview with engineer. Interviewer was very nice, talked about my previous work and his previous work. Then got into coding questions.

Interview Question – Given a list of k sublists containing n sorted integers, generate output as one sorted list.
Comment on complexities.
  View Answers (3)

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Glassdoor is your free inside look at Facebook Software Engineer interview questions and advice. All 314 interview reviews posted anonymously by Facebook employees and interview candidates.