This was a concurrency and thread-focused coding round, non-LeetCode style. The questions were difficult.

Sometimes, within the same problem, you might be asked to implement trivial thread-safe data structures instead of using built-ins, and then use them.

Overall, I found it very interesting and loved the interview, although I was rejected. The discussion was productive.

There is a single bathroom to be used in a voting agency for both Democrats (D) and Republicans (R).

This single bathroom can accommodate a maximum of 3 people.

Each person takes f(N) seconds to do their business. f(N) is a function of the person's name and returns a varying number.

Conditions:

• At any given time, the bathroom cannot have a mixed set of people.
• The bathroom can have at most 3 people.
• The following combinations are not allowed: (2D, 1R) or (1D, 1R).
• The following combinations are allowed: (), (3D), (2D), (1R) – meaning pure Republicans or pure Democrats.

While the bathroom is occupied, people are to wait in a queue.

What is the most optimal system for managing people in this queue so that the most eligible person instantly gets to use the bathroom whenever there is room, based on the above conditions?