Google Software Engineer Interview Experience — L4 Most-Active-User Coding Went Fine, Rejected After a Relentless BQ Round

Coding:

There are different messages, undirected (A, B). I had to write a method register to store these messages, and another method mostActiveUser() that computes and returns the person who has messaged the most users. I clarified the problem, used a hashmap, and finished writing it quickly. For space complexity I said O(N) at first, but he pointed out that every key maps to its own set, and I immediately corrected it to O(N^2). Follow-up 1 was to optimize the second method to O(1). Wrote that quickly too, kept communicating the whole time, and explained what I was doing at every step. Follow-up 2 asked how to return the top K. I said use a PQ with a fixed heap size. He said k can change, so I said then it's N log(N). He described a faster solution, which I didn't really follow.

BQ:

The interviewer asked lots of variations and unconventional questions. These are the ones I remember:

1. Tell me about a time when you had more tasks than you expect.

   I answered with a time I had two urgent tasks and how I managed them. Then the interviewer followed up on why that approach worked. After I answered, the interviewer followed up asking what the customer impact was. After I answered that, they kept pushing: why did you end up with two urgent tasks in the first place, and why didn't you confirm earlier that they didn't conflict?

2. Tell me about a time when you had to change direction midway through a project.

   I talked about splitting one set of user data into three and displaying them separately, which I worked out with the PM because there was a technical performance problem. Then the interviewer followed up asking how I confirmed it with users. I said that as a developer I only sign off on the technical side, and the PM confirms whether it's acceptable. Then the interviewer followed up: besides the PM, how would you evaluate this metric? (No idea, we never actually had that step back then.)

3. If the people on a team already get along well, how do you make the team more innovative?

   Didn't answer this one well, I had never prepared for it at all. I made something up about doing more team-building activities, pulling everyone into a group chat to brainstorm and share different ideas.

4. Tell me about a time you helped someone fit into the team.

   I answered with my experience mentoring someone. Then the interviewer followed up saying that was technical, did I have anything on the career side? I thought for a while and couldn't come up with anything...

Got a rejection a week later. Personally I think I failed the second round. I didn't expect BQ to be asked in this much detail. Next time I prepare I really need to think through every aspect of each project, because trying to come up with it on the spot, you really just can't...