Education: Bachelors in Computer Science
Experince: ~6 years with Amazon
Localtion: Seattle
Timeline: Interviews from first week of March to first week of April

Contact from recruiter
I was reached out by the recruiter during the last week of February to see if i was interested in an Android role at Facebook. I told him i was not and am looking at infra kind of roles. The recruiter connected me to another one who scheduled a Phone screen in the first week of March.

Phone Screen
This was a 45 minute round and the interviewer indicated that he would ask me 2 questions and to adjust my time accordingly.
First Question

• Given a mathematical expression write code to - validate the expression, convert it to postfix and evaluate the postfix expression.
• https://leetcode.com/problems/word-break-ii/ - i only gave the brute force solution and when time was running out talked through the optimization of using a map.

Overall, i felt very hard to write the code for the above in ~40 minutes. I definitely would not be able to if i did not know the approaches before hand. The interviewer was very particular about syntaxing and wanted a ready-to-run code.

I got a call in a week saying that they are considering me for virtual onsite and asked me to give dates.

**Onsite **
First Round

• Given a linked list, reverse every 'k' elements.
• Given an array, find the counts such that (i<j and a[i] > a[j]). -- I gave a brute force solution and did not know the optimal. The interviewer tried to give me a hint of using merge sort but I was unable to come up with a working solution.

Second Round (Manager Round)
Ton of LP questions. I would suggest you have a prepared list of answers to the most common questions. That should be more than enough for this round.
The person i talked to on the other side was having a very strong spanish accent and it was very hard for me to understand him and vice-versa. We easily wasted 15 minutes just repeating what we spoke.

Third round

• Given a file system volume, write an algorithm to defragment it. Assume the memory chunks in the file system can be represented as a linked list. Followup: Given two volumes, compare if they are equivalent...
  This question seemed very open-ended. I felt like the interviewer had a solution in mind and wanted me to come up with it. He wanted to me come up with a structure for memory chunk and contents etc...
  The followup ultimately was just comparing 2 linked lists for equality.
• Modification of https://leetcode.com/problems/nested-list-weight-sum/

Fourth round (Design)
I feel this is the round that made the most difference. I sort-of-bombed it and also the communication b/w the interviewer and me was non-existent.
Question : Design a system that can ingest facebook statuses and run billions of queries against those statuses.
To be honest, i have very good knowedge of this type of system as i have worked on similar one at amazon and also prepared before the interview (*** the design , twitter talks , lucene talks etc...)
The biggest mistake i made was that i went deep into a single area and did not really take it step by step. The interviewer tried once/twice to ask questions to make me answer what he wanted but i guess i got carried away. His very thick asian accent did not help either.
My suggestions for this would be to have mock interviews with peers/friends and also start with the basics.
For eg.. we discussed A-Records and CNAMES somehow but not Load Balancing in detail ... :(

Fifth Round

• A very modified problem similar to https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/. If you had done this, you would do it easily.
• https://leetcode.com/problems/divide-two-integers/ --- I bombed this question completely. I always felt like this is a bad question to ask in an interview setting and never saw the approaches. I was able to answer the brute force(subtraction) and the power of 2 solution but missed a lot of edge cases. (The interviewer sort of wanted me to cover cases involving signed/unsigned ints/longs etc...)

Overall, i think the interview is not very difficult compared to an L5 interview at amazon. The difference is that FB expects you to write pitch-perfect code while at Amazon, you are given some leeway as long as your algo is right.
Gotta blame myself, i did not prepare very seriously (leetcoded for a week or so and did only the FB questions). A bit disappointed but am okay.

Lessons learnt

• Leetcode 2-3 problems everyday. Dont become rusty especially in times like these.
• Write in a text editor and make sure you get it right in the first couple of runs.
• Improve communication. You might know a lot of stuff but it does not matter if you cannot articulate it.
• Practice design interviews by discussing ideas with friends ... listen to talks .