FB Interview Experience Part 3: On-Site Interviews

This is my final post in my facebook interview series. This comes after:

My final on-site interviews were scheduled on the 9th October in the London Office on something people at facebook call “University Day”. Its mostly a day for interviewing undergrads or people who have just finished their undergrad.

Note: I’m not allowed to reveal the interview questions.


From what I had read online, I knew that the Software Developer Role had 3 on-site interviews of 45 minutes each:

  • Behavioural
  • Algorithmic
  • System Design

I hadn’t prepared anything specific for the behavioural interview.

I spent the majority of the time preparing for the algorithmic interview as it is by far my weakest point. I’m a developer who likes to develop things and I do have knowledge of data structures and algorithms but I usually look them up when needed and sometimes even solutions to simple algorithmic problems don’t come easily to me. (I practised from leetcode, hackerrank and Elements of Programming Interviews)

For the system design interview, I had taken a look at some sample problems online and had decided that I would take a closer look at them at a later stage as they seemed to be the kind of problems I enjoy solving and would be able to grasp the idea easily.

Later on (I don’t remember exactly when), I took a closer look at my interview confirmation mail and got to know that since I’m an undergrad, instead of the system design interview I would have another algorithmic interview (bummer!).


I reached the venue at the specified time and there were a total of 7 people who were interviewing that day. There were people who were still doing their undergraduate (like me) and others who had just finished in May and had recently joined some other company. We were welcomed by the wonderful recruiting team and then after a few introductions, were given a schedule of the interviews. I had the interviews in the following order:

  • Behavioural
  • Algorithmic 1
  • Algorithmic 2

Behavioural Interview

The initial 20-30 minutes were discussions on my past experience - stuff like explaining any project I had done, my particular role, why I chose to explain that particular project now, issues I might have faced while working under someone, while mentoring someone and so on. Some examples of the type of questions asked are available at the following link.

After that, we had time for a simple algorithmic problem as well which I was supposed to solve on a whiteboard. The problem was a pretty basic algorithm wrapped up in a real world use-case and I was able to solve it quickly. First I verbally explained my solution and then implemented it on the whiteboard.

Algorithmic Interview 1

This was one of the interviews I think I messed up in. Usually in 45 minute interviews, you have 2 problems which are usually solved in the timeframe and then if there is extra time remaining, you get another question on which usually a discussion is just started. I solved the first (easy) question and then got stuck on the 2nd one. Even when I managed to solve it, the solution wasn’t optimal. But, somehow, even though very little time was left, I managed to atleast verbally/diagrammatically on the whiteboard, solve the last one.

For the second question, I initially wasn’t able to think of any solution and ended up explaining the brute force solution (my fallback when I’m unable to think of anything). Even after further discussions and hints from my interviewer, I arrived at a O(nk) solution even though the optimal solution would be O(n). I ultimately wrote this non-optimal solution on the whiteboard.

The third question was a pretty nice question and I managed an optimal O(n) solution. We ran out of time before I could write down the whole solution but I managed to logically explain my idea.

Algorithmic Interview 2

This third interview also went pretty well. We managed to finish 10 minutes before time. After I solved each question, the interviewer asked what test cases would you pass to make this program break and also while solving he asked me to do proper edge case handling via throws.

Once I was done with the questions (explaining idea + code), the question was modified as a test of how well I had written my code to adjust for modifications for a slightly different input and output.

For the 2nd question, I was stuck for some time but once I was given a hint - to think on what algorithm I was mentally applying to achieve this series, I managed to solve it and write a pretty elegant solution, if I might say so. My code was structured good enough for me to make a single line change and add a throw at some spot to handle the variant of the question asked to me.

Post Interview

After the interviews, we were given an explaination of how the interviews were reviewed and then we were taken on the tour of the office (spoiler alert: its awesome!!) and that was it. The whole interview process was now done.

I was eventually contacted and informed that I would be extended a full-time offer at the London Office. Right now, I have accepted the offer and am really looking forward to joining there in August this year. Its going to be an amazing experience and I really hope I’ll learn a lot from it.

Best mail I’ve received in my life!!

Best mail I’ve received in my life!!