Recently I gave interviews for Google L4 Position in Hyderabad

Recruiter reached out to me on LinkedIn to check my interest
I took around 4 weeks for preparation and I requested for a mock interview during the same time

Mock Interview:
I was asked Maximal Square (DP) question. I was able to solve the question easily (I solved it in Leetcode before)
Feedback: Positive
Interviewer herself gave the feedback during the interview since its a mock. She told me I did very well and I am ready for Phone Screen and Onsites
She told me to follow few things while solving like covering edge cases, variable names, function names

Phone Screen:
I was asked a Binary Tree question where there are weights on edges between nodes and I am supposed to find minimum cost to cut all the leaf nodes from the root.
It was DP question. I was able to solve it
Feedback: Positive

Recruiter called me after a day and told me I was selected for Onsite rounds as my screening round feedback came positive

Onsite-1:
Question was simple I was given a List of Booking Records from last year.

class Records {
int id;
int startTime;
int endTime;
}

I am supposed to return List of Assignments of cars such that I use minimum number of cars to fullfill all the booking requests

class Assignment {
int carID;
int recordID;
}

I sorted the records on startTime and used a min-heap to find earliest car that will be able to finish the request based on endTime.
Using this approach I was able to solve it
Followup: Return minimum number of cars instead of assignments
Feedback: Positive

**Onsite-2: **

Again an easy question. I was given a list of messages

class Message {
String content;
int receivedTime;
}

I should return a list of messages which shouldn't contain any duplicate messages within 10 seconds after the first message is received (First message can be present in the list)
I used a HashMap to keep lastTimeReceived for any message and used the same to compare the next messages
Followup: Now I should remove all the duplicates within 10 seconds even the first message shouldn't be present
Feedback: Positive

Recruiter called me after 2nd onsite and told me both onsites came positive.
I was so happy thinking all my luck and everything is falling in place.

Onsite-3:
Interviewer asked me this question https://leetcode.com/problems/number-of-closed-islands/description/ only difference is he used '.' & 'x' instead of 0 and 1 to denote water and land.
Luckily I was able to solve it because I know the question and I solved it before. I used BFS to solve it

But my bad luck is that interviewer doesn't know the solution to it. I don't why he picked a question for which he doesn't know the solution.
I think he just thought its a hard question and I will not be able to solve it. But I did. I explained him the entire code with a dry run

Now how do I know my code works
Google takes its interviews on Google Docs. We can't compile it there and it doesn't show any syntax errors. During the mock interview feedback, the interviewer told me about this and told me to be careful while writing the code.
I did this check after every interview. I copied the entire code in my clipboard and checked it later to see if I missed anything, I never missed anything.

For the last round, similarly I copied the code and since I saw the question before in leetcode. I ran the same code in leetcode. I changed nothing except for the '.'/'x' notation to match 0/1 notation and it passed all the test cases

And he gave the feedback as negative saying I didn't cover all the cases and I lost the offer for this. Atleast he could have given Lean Hire but no straight away Negative

I don't know why these type of people volunteer to take interviews and reject candidates for nothing.
I don't know how he is working at Google and who hired him.

Your talent itself is not enough even the interviewer should also be in a state to understand your solution.

I even told the HR when she called me to inform the feedback. But nothing's in her hands