System Design Interview Problems & Solutions
Real-world system design interview problems with detailed solutions, iterations, and trade-off analysis.
📁 Structure
Each problem includes:
- Problem statement with requirements
- Clarifying questions to ask interviewer
- Capacity estimation (QPS, storage, bandwidth)
- Multiple design iterations (v1 → v2 → v3)
- Deep dives into critical components
- Final architecture with scalability considerations
- Alternatives comparison table
- Trade-offs and decisions
🎯 How to Use
Before Interview
- Read problem without looking at solution
- Set 45-min timer, design on paper
- Compare your approach with solution
- Note what you missed
During Practice
- Follow the 4-step framework (interview-framework)
- Think out loud as you read
- Draw diagrams for each iteration
- Focus on trade-offs, not perfect solution
After Practice
- Review alternatives table
- Understand why certain choices were made
- Practice explaining the design out loud
- Redo the problem 1 week later
📚 Problem Categories
Data-Intensive Systems
- Tax Refund Status Portal ✅
- Stock Trading Platform
- Healthcare Records System
User-Facing Applications
- Video Streaming Platform
- Social Media Feed
- Ride-Sharing Service
Infrastructure & DevOps
- Metrics & Monitoring System
- Distributed Task Scheduler
- CI/CD Pipeline
E-commerce & Fintech
- E-commerce Platform
- Payment Gateway
- Fraud Detection System
Real-Time Systems
- Chat Application
- Multiplayer Game Backend
- Live Sports Score Update
🎓 Difficulty Levels
- Easy (30-35 min): Single region, <10K QPS, 2-3 core components
- Medium (40-45 min): Multi-region, 10-100K QPS, 5-7 components
- Hard (50-60 min): Global scale, >100K QPS, complex trade-offs
📊 Problem List
| Problem | Difficulty | Category | Key Concepts | Companies |
|---|---|---|---|---|
| Tax Refund Portal | Medium | Data-Intensive | Encryption, Gen AI, Global Scale | Government, Fintech |
| Stock Trading Platform | Hard | Real-Time | Low latency, Strong consistency | Trading firms |
| Healthcare Records | Medium | Data-Intensive | HIPAA, Security, Audit logs | Healthcare |
🔑 Key Patterns to Master
Each problem demonstrates specific patterns:
- Security-First Design: Tax Refund Portal
- Low-Latency Systems: Stock Trading
- Strong Consistency: Payment Gateway
- Eventual Consistency: Social Feed
- Real-Time Updates: Chat, Live Scores
- Heavy Read: Content platforms
- Heavy Write: Logging, Metrics
- Geo-Distributed: Global applications
📝 Interview Success Tips
What Makes a Good Solution
✅ Asks clarifying questions first
✅ Does back-of-envelope calculations
✅ Iterates through multiple designs
✅ Explains trade-offs clearly
✅ Considers failure scenarios
✅ Discusses monitoring & operations
✅ Mentions cost implications
Common Mistakes to Avoid
❌ Jumps to complex solution immediately
❌ Doesn’t ask about scale/requirements
❌ Ignores security/privacy
❌ No discussion of alternatives
❌ Forgets about operations/monitoring
❌ Over-engineers simple problem
🔗 Related Resources
- Framework: interview-framework - 4-step approach
- Estimation: estimation-cheatsheet - Numbers & calculations
- Components: distributed-system-components - Building blocks
- Patterns: key-patterns - Reusable designs
Practice 3-5 problems per week. Focus on explaining your thinking, not memorizing solutions.
Last Updated: 2026-04-09