Design coding platform with global leaderboard
Company: Meta
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
## Scenario
Design a LeetCode-like online coding practice platform that also has a **global leaderboard** (e.g., Top K users by score) and can show a user’s rank.
## Functional requirements
- Users can:
- Browse problems.
- Submit code for a problem in a chosen language.
- Receive verdicts (Accepted/Wrong Answer/Time Limit, etc.) and runtime/memory stats.
- The system maintains a **leaderboard**:
- Score model is flexible (e.g., points per solved problem, bonus for difficulty, penalties for wrong submissions).
- Support queries:
- `GetTopK(k)` (global and optionally per region/time window).
- `GetUserRank(userId)`.
## Non-functional requirements
- High throughput during peaks (many submissions at once).
- Low-latency reads for Top K leaderboard.
- Correctness and anti-cheat considerations.
- Observability: be able to identify bottlenecks and scale the right components.
## Deliverables
1. High-level architecture and main services.
2. Data model (what is stored where).
3. APIs for submission + leaderboard queries.
4. How leaderboard updates are computed and served efficiently.
5. Identify likely bottlenecks and how you’d improve them.
Quick Answer: This question evaluates proficiency in scalable distributed systems and system design, including real-time ranking algorithms, data modeling, API design, throughput and latency trade-offs, correctness and anti-cheat considerations, and observability for a coding platform with a global leaderboard.