Design a fair event registration queue API

Q: Design a fair event registration queue API

This question evaluates a candidate's ability to design an in-memory, FIFO event registration service using object-oriented design, testing knowledge of data structures, state management, and efficient removal operations.

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Question

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Scenario

Design an in-memory service (OOD-style) to manage registrations for an event where fairness means users are served strictly in the order they registered (FIFO).

Users can:

Register for the event
Unregister (cancel) their registration
Query the first k users in the current fair order

Required API

Define and implement these operations:

register(userId)
unregister(userId)
topK(k) -> List<userId> (return the earliest k currently-registered users)

Expectations

Preserve original registration order among active users.
Handle unregister efficiently.
Discuss time/space complexity and key edge cases (duplicate register, unregister missing user, etc.).

Design a fair event registration queue API

Scenario

Required API

Expectations

Solution

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Design a fair event registration queue API

Overview

Scenario

Required API

Expectations

Solution

Comments (0)