Y.O.E: ~5 years
Current Job: Mid-Big size company

Got a message on LinkedIn from a recruiter for a position based in London for fb. I was very happy to get an opportunity to interview with fb. Recruiter scheduled a call for introduction two days later. Talked about my current project and interests.

Phone Interview:

1. Very easy question based on some tax brackets (solved)
2. string based question, LC easy (solved)

Then got a confirmation mail the following day after the interview, that they want to do a virtual onstite round. Got a month of time to prepare and brush up.

Round 1 - Coding:

1. LC Easy - string based question (similar to verifying alien dictionary) (solved)
2. LC medium - find K closest points to origin (solved with prority queue based approach discussed that its avg TC is O(nlogn), and discussed the algo for quick-select approach and mentioned that in the worst case quick-select can give n^2 TC).

Round 2 - Behavioural ( &technical ) :
Can't recall all of them,

1. Project that you are most proud of
2. Tell me about a time when you had a disagreement with your collegue / manager
3. Tell me about a time when you were wrong, what were your learnings from the experience.
4. What are the things you will be improving or already improving
5. This was a technial questions - given a stream of data where only 1 element occures odd number of time and every other will occur even number of time. How would you identify the odd occuring one. (solved with XOR based approach, explained him with examples, follow up questions, how would you ensure the validity of data. Answered that if the current state of data stream is valid then current XOR would either be zero the number which came recently.)

Round 3 - System design :
Design something similar to fb news feed, follow up questions - bottleneck of the services, alerting & monitoring, deeped dive into API structures. The interviewer seemed happy with all my answers

Round 4 - Coding :

1. can't recall exactly but the question was LC medium (some sort of forming lexicographically largest string after atmost 1 swap and then followed up for atmost K swaps) (Solved)
2. Given list of points on X Y plane, find the maximum area of the rectangle that can be formed connecting any 4 points in. (Solved)

I haven't heard back from them even after almost 3 weeks. Can't think of any reason for them to reject me. But disappointed with the experience after the interview. The companies should not delay, because it affects the candidates further preparation and work in a very significant manner. And specially if its a rejection you should not hold it for longer. But who knows whats happening at the other end.

Update: After a long waiting time, I got this unfortunate news from the recruiter that they got many posititive singnal but in the end they decided not to offer this time.