Design an online coding contest platform

Q: Design an online coding contest platform

This is a System Design interview question from Meta for Software Engineer roles. View the full question and solution on PracHub.

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Question

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Design a platform to host timed programming contests (similar to weekly/biweekly coding contests).

Core scenario

Users register for a contest, read problems, submit solutions during a fixed time window.
The system judges submissions, computes per-problem results (AC/WA/TLE/etc.), and produces a live leaderboard.

Requirements

Functional

Contest lifecycle: create contest, schedule start/end, publish problems.
User participation: registration/eligibility, start contest, view problems.
Submissions: accept code, compile/run, return verdict + runtime/memory.
Scoring & ranking: points/penalties, tie-break rules, frozen board near end (optional).
Live updates: near-real-time leaderboard.
Anti-cheat basics: rate limiting, plagiarism signals (high-level).

Non-functional

High concurrency at start and near deadlines.
Strong isolation/security for running untrusted code.
Reliability: submissions must not be lost; judge results must be auditable.
Low latency for submission acknowledgment; judging latency can be seconds.

Deliverables

Explain your high-level architecture, key services, data storage choices, queueing/judging pipeline, and how you scale and keep the leaderboard correct.