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Current Status: Senior Software Engineer
Experience : 6 YOE
Position: E5 at Facebook London
Date: June 2021
LeedCode : 400+(60% medium, 20% hard, 20% easy)

I am not posting exact questions due to NDA

Facebook -> It took 4 months due to covid for complete interview
Phone Interview :
i was asked only one question, it was medium LC question. I was given a string and i have to find the palindrominc substring in that string(Longest). Given my initial toughts on this question added some test cases and solved, with complexity explained
Result -> positive feedback, moved to virtual onsite rounds, i have taken one month from HR for more preparation

After One Month : when i was going to have my onsite rounds, a week before that i was diagnosed with COVID-19, explained the situation to HR and she cancelled event for the time being. connected to HR after one month and spoked to her about covid, how i was not able to concentrate on this thing. got very weak due to covid and not able to prepare for onsite as well
but i suggested HR to schedule after 2 months (so total it took 3 months for on site Interview)

Onsite R1 : Coding
Q1 : it was again related to valid palindrom string question with followup question -> got clarity added testcases and solved(LC Easy)
Q2 : Lowest Common Ancestor of binary with with given only two nodes and parent information is available with the node, took some time to understand and gave some test cases, multiple approached given after rethinking interviewer accepted my approach and solved the question (LC Medium)
Result : Positive

Onsite R2 : Coding
Q1 : MagicMap design question with given api, tricky part was to implement a function which have putAll functionalty in map, so that every entry gets updated, given optimal approach and solved the question (LC Easy)
Q2 : an interger is given and we need to convert that interger to string value, it was a LC hard question, (LC Medium)
there are multiple cases which u can miss, but coved all the cases first told the interviewer and coded in time
Result : Positive

Onsite R3 : behavioral
was asked about all the general question that was asked in every company, interviewer looked satisfied with my answer
Result : Positive

Onsite R4 : System Design
interviewer asked me to create a chat application, i have asked the questions for requirement clarification, have done tradeoffs, designed HLD and LLD, designed API as well
though i have missed one cases which was very critical and interviewer told me about that later i realised may be this should have to be asked before to interviewer
Result : Not suitable for E5(also this was specific to E5 only, not E4 thats why got rejection)

I was not good in the system design according to recruiter, some part was good but for thinking the critical cases i was not able to comeup by my self, i realized at that time only that i have missed this chance to make it to facebook due to system design.

Update : The things that i was missing in system design was, i was not able to comeup with the sync to all the screens, if user has received a message from anyone it should be notified to all the active screens in the app, i have missed this case, as this was the main concept behind every chat app that it should be synced everytime u receive any update, i made this major mistake.

but i was very happy that i have made it to that stage in facebook

Also guys my personal opinion Leetcode halped me a lot not just for facebook, but for other companies too. I have got multiple offers in hand, will try my luck next time with facebook.
also best of luck guys who is trying for facebook.

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