Caching Strategies Explained with Interview Examples

Trade-offs: Encryption for data vs. performance. From GeeksforGeeks: “Tests error handling in 15% of interviews.”

8. Design a Library Management System

Track books and users. Requirements: Borrow/return, fine calculation, search. Non-functional: Fast lookups.

Components:

• Classes: Library, Book, User, Librarian.
• Methods: issueBook(), returnBook().

Trade-offs: HashMap for catalogs vs. databases. Tip: Add notifications for due dates.

9. Design Splitwise (Expense Sharing)

Group expense tracking. Requirements: Add expenses, settle balances, user groups. Non-functional: Accurate calculations.

Components:

• Classes: User, Group, Expense, Balance.
• Methods: addExpense(), settleUp().

Trade-offs: Graph for debts vs. matrices. Link to our crash course for quick prep.

10. Design a Movie Ticket Booking System

Real-time seat reservation. Requirements: Seat selection, booking, payment. Non-functional: Concurrency handling.

Components:

• Classes: Cinema, Screen, Seat, Booking.
• Methods: bookTicket(), checkAvailability().

Trade-offs: Locks for seats vs. optimistic concurrency. From DEV Community: “Common in 25% of LLD questions.”

Top 10 HLD Questions for SDE-2 Interviews

These focus on scalability and distributed systems. Expect discussions on databases, caching, and load balancing.

1. Design a URL Shortening Service (TinyURL)

Scale to millions of URLs. Requirements: Shorten, redirect, custom URLs. Non-functional: High availability (99.9%), low latency (<100ms).

Components:

• Load balancer, API servers, database (NoSQL for scale), cache (Redis).
• Use base62 encoding for shorts, MD5 hashing for uniqueness.

Trade-offs: SQL vs. NoSQL—NoSQL for sharding. From Educative: “Asked in 40% of HLD interviews.” Tip: Calculate storage needs (e.g., 1B URLs = ~10TB).

2. Design Twitter (Social Media Feed)

Handle tweets, follows, timelines. Requirements: Post/read tweets, real-time feeds. Non-functional: Scale to 500M users.

Components:

• Fanout service for feeds, Kafka for messaging, Cassandra for storage.

Trade-offs: Push vs. pull feeds. Quote from GitHub primer: “Tests hybrid models for celebrities.” Integrate with our data science course for recommendation engines.

3. Design Uber (Ride-Sharing)

Location-based matching. Requirements: Request rides, match drivers, ETA calculation. Non-functional: Real-time, fault-tolerant.

Components:

• Geospatial DB (PostGIS), quadtrees for location, WebSockets for updates.

Trade-offs: Monolith vs. microservices. From Medium: “Appears in 30% of FAANG SDE-2 rounds.”

4. Design WhatsApp (Messaging App)

End-to-end chat. Requirements: Messages, groups, media. Non-functional: Low latency, encryption.

Components:

• XMPP protocol, Erlang for concurrency, SQLite for local storage.

Trade-offs: WebSockets vs. long polling.

5. Design YouTube (Video Streaming)

Upload/view videos. Requirements: Streaming, recommendations. Non-functional: Handle 5B views/day.

Components:

• CDNs for delivery, Hadoop for analytics, ML for recs.

Trade-offs: Adaptive bitrate vs. fixed.

6. Design an API Rate Limiter

Prevent abuse. Requirements: Limit requests per user/IP. Non-functional: Distributed scale.

Components:

• Token bucket algorithm, Redis for counters.

Trade-offs: Sliding window vs. fixed.

7. Design a Distributed Cache (Like Memcached)

Fast data access. Requirements: Get/set, eviction. Non-functional: Consistency.

Components:

• Consistent hashing, LRU eviction.

Trade-offs: Replication vs. partitioning.

8. Design a Notification System

Push alerts. Requirements: Email/SMS/push. Non-functional: Reliable delivery.

Components:

• Kafka queues, workers for channels.

Trade-offs: At-least-once vs. exactly-once.

9. Design a Recommendation System (Netflix-like)

Personalized suggestions. Requirements: User history-based recs. Non-functional: Real-time.

Components:

• Collaborative filtering, Spark for processing.

Trade-offs: Content vs. user-based.

10. Design a Web Crawler

Index web pages. Requirements: Fetch, parse, store. Non-functional: Polite crawling.

Components:

• URL queue, robots.txt checker, Bloom filters for duplicates.

Trade-offs: Breadth-first vs. depth-first.

Additional 20 Commonly Asked System Design Questions

To round out your prep, here are 20 more questions from real interviews (sourced from Educative, DEV Community, and GitHub). Each includes a brief in-depth outline.

1. Design Instagram: Focus on photo uploads, feeds, stories. Use S3 for storage, Redis for timelines. Trade-off: Infinite scrolling pagination.
2. Design Netflix: Video transcoding, AB testing. Components: AWS Elemental, ML models. Tip: Discuss bandwidth optimization.
3. Design Google Maps: Routing, traffic. Use Dijkstra’s algorithm, real-time data feeds.
4. Design Pastebin: Text storage/sharing. Encryption for privacy, TTL for expiration.
5. Design a Distributed Key-Value Store: Like DynamoDB. Ring hashing, eventual consistency.
6. Design Tinder: Swiping, matching. Geohashing for location, push notifications.
7. Design Spotify: Music streaming, playlists. Offline sync, collaborative editing.
8. Design a Content Delivery Network (CDN): Caching, edge servers. Anycast routing.
9. Design a Pub/Sub System (Kafka-like): Topics, brokers. Partitioning for scale.
10. Design an Authentication System (Auth0-like): SSO, JWT tokens, MFA.
11. Design Dropbox: File sync, versioning. Chunking uploads, delta encoding.
12. Design a Job Scheduler: Cron-like, distributed. Quartz framework inspiration.
13. Design a Search Autocomplete: Trie structure, frequency ranking.
14. Design a Vending Machine (LLD variant): State machines, inventory DB.
15. Design Amazon E-commerce: Cart, payments. Microservices, eventual consistency.
16. Design a Conference Room Booking System: Calendar integration, conflict resolution.
17. Design a Food Delivery App (DoorDash-like): Order tracking, ETA predictions.
18. Design Google Docs: Real-time collab. Operational transformation.
19. Design a Stock Exchange System: Matching engine, low-latency queues.
20. Design a Distributed Web Crawler: URL frontier, politeness policies.

These additional questions often appear in mixed rounds—practice by mocking interviews. For full mastery, join our master course.

Wrapping Up: Actionable Steps to Ace Your Interview

You’ve now got a deep dive into 30+ system design questions, complete with strategies to tackle them. Remember, interviews are conversations—clarify assumptions and discuss trade-offs to show expertise. Practice sketching designs on paper or whiteboards, and time yourself for 45-minute simulations.

Ready to level up? Dive into our crash course for hands-on projects. What question challenged you most? Share in the comments, and let’s discuss!

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