Design user communication functions
In-Memory Communication Manager
Context
Build a simple in-memory component that tracks which users can communicate with each other. Treat a communication link between two users as an undirected connection (if A can talk to B, then B can talk to A). Assume user IDs are hashable (e.g., strings or integers) and that the system runs in a single process.
Requirements
Implement the following functions:
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connect(user_a, user_b): Create a bidirectional connection so the two users can communicate.
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disconnect(user_a, user_b): Remove an existing bidirectional connection, if present.
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clear(): Remove all existing user communications.
Also:
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Describe the data structures you use.
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Provide code for the above API.
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Analyze the time and space complexity.
Assumptions
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Connections are undirected and idempotent (calling connect twice for the same pair should not create duplicates or errors).
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Self-connections (a user connected to itself) should be rejected or ignored.
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Disconnecting a non-existent connection should be a no-op.
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Creating a connection for users not yet seen should implicitly add them to the system.
Constraints & Assumptions
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Preserve the scope, facts, inputs, and requested outputs from the prompt above.
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If the prompt leaves a detail unspecified, state a reasonable assumption before relying on it.
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Keep the answer interview-ready: concise enough to present, but concrete enough to implement or evaluate.
Clarifying Questions to Ask
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Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
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State explicit assumptions before making sizing or architecture decisions.
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Prioritize the functional path first, then address reliability, security, observability, and rollout.
What a Strong Answer Covers
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A scoped requirements summary with concrete non-goals and success metrics.
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API, data model, architecture, consistency, capacity, and operations.
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Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
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A validation, monitoring, migration, and launch plan appropriate for the risk level.
Follow-up Questions
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What breaks first at 10x traffic or data volume?
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How would you degrade gracefully during dependency failures?
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What metrics and alerts would prove the design is healthy after launch?