Three rounds were scheduled: the first was pure technical, the second was technical and mostly System Design, and the third was with the Engineering Manager.

A SDE 3 took the first round. He was a chill, wholesome guy and told me to be friendly and not be nervous. He started with a discussion on my projects, covering the "what, whys, and hows." We discussed WebSockets and authentication, then designing a rate limiter for an API gateway, optimized with Redis.

Then we moved to DSA. He asked two simple questions. One involved strings and arrays, which I solved and optimized, but the best solution was with Tries, which I gave. Some simple SQL and NoSQL discussion followed, then some networking and throttling. It ended with a general discussion on culture and expectations.

I was expecting that I cleared this round and was very confident for the System Design round.

Well, I couldn't clear it. What I think is they expect full clarity and almost perfect answers, so if you seem a little confused or not direct, it won't help.

Designing and optimizing a rate limiter

Given a 2D vector of characters (0, 1, 2) and another vector of strings made of characters (0, 1, 2), I have to search 1D vectors in the first 2D vector corresponding to strings in the second vector. The question was modified; different conditions and constraints were given after every solution.