The best structured roadmap for LeetCode prep. 150 + 250 problems organized by pattern with video explanations. Start here.

Industry-standard interview prep platform. Focus on Medium problems. Use filters for company tags when targeting specific companies.

Animated visualizations of data structures and algorithms. Essential for understanding how sorting, trees, and graphs actually work step-by-step.

The definitive textbook. Rigorous proofs and analysis. Use as reference for complex algorithms — not as a primary study guide.

Comprehensive algorithm reference with implementations. Excellent for graph algorithms, number theory, and competitive programming topics.

Free, curated guide to the tech interview process — resume, behavioral, coding, system design. Maintained by ex-Meta engineer.

The most-starred system design resource on GitHub. Covers scalability, CAP theorem, databases, caching, and full design walkthroughs. Free.

The best book for distributed systems and databases. Covers replication, partitioning, consistency, consensus. Required reading for senior roles.

By the author of "System Design Interview" books. Beautiful visual diagrams of real systems. Newsletter and YouTube channel are free.

Real architecture case studies from companies like Twitter, YouTube, WhatsApp. Learn how production systems actually scale.

Beautifully illustrated guide to all 23 Gang of Four patterns plus refactoring techniques. Best visual reference for LLD and OOP design.

Curated list of system design resources including papers, articles, and courses. Great starting point for structured HLD prep.

The authoritative source. Handbook covers everyday types, narrowing, functions, and more. Reference section covers all compiler options.

Deep dive into TypeScript by one of the best educators. Free workshops on generics, type transformations, and advanced patterns. Highly recommended.

LeetCode-style challenges for TypeScript types. Work through Easy → Hard to master mapped types, conditional types, and infer. Great for interviews.

Spaced repetition learning for TypeScript. Short interactive lessons that test your knowledge over time. Excellent retention method.

The definitive Java programming guide. 90 items covering best practices for generics, lambdas, concurrency, and serialization. Must-read for Java interviews.

All GoF patterns with Java code examples. Strategy, Observer, Factory, Singleton, Builder — with UML and real-world use cases.

Official Oracle tutorials covering all Java fundamentals. Excellent for generics, collections, concurrency utilities, and I/O streams.

Practical Java and Spring tutorials. Deep dives into Java concurrency, streams, optional, and Spring Boot. Great for quick topic lookups.

Free Kafka courses by Confluent (Kafka's creators). Covers producers, consumers, Kafka Streams, Schema Registry, and ksqlDB. Best structured learning path.

Official deep-dive by Confluent engineers. Covers internals, replication, exactly-once semantics, and operations at scale. Free PDF on Confluent website.

Official reference. Use for configuration options, consumer group mechanics, log compaction, and MirrorMaker 2 for multi-region setups.

Free CMU database course with full lecture videos. Covers storage engines, B-Trees, query execution, concurrency control (MVCC, 2PL), and recovery (ARIES).

Free guide to SQL query performance and database indexing. Explains B-Tree indexes, composite indexes, index-only scans, and common pitfalls.

Official MongoDB reference. Essential for understanding document model, aggregation pipeline, indexes, transactions, and sharding.

Redis data types (Strings, Hashes, Lists, Sets, Sorted Sets, Streams), persistence modes, eviction policies, and Pub/Sub patterns.

Clear explanations of database sharding strategies, consistent hashing, and distributed SQL. PlanetScale blog has excellent deep-dives.

The best free OS textbook. Covers virtualization (processes/memory), concurrency (locks, semaphores, condition variables), and persistence (file systems).

The definitive guide to Java concurrency by Brian Goetz. Thread safety, Executor framework, atomic variables, locks, and testing concurrent programs.

Study the classic synchronization problems: Producer-Consumer, Dining Philosophers, Readers-Writers. These appear directly in interviews.

Official Docker tutorial. Covers containerization concepts, Dockerfile best practices, multi-stage builds, Docker Compose, and networking.

AWS's five pillars: Operational Excellence, Security, Reliability, Performance, Cost Optimization. Essential for architecture design questions.

Official Kubernetes tutorials. Learn Pods, Deployments, Services, ConfigMaps, Secrets, Ingress, and Horizontal Pod Autoscaling.

One-page visual cheatsheets for every major AWS service. Perfect for quick review before interviews. Clean, printable diagrams.

Comprehensive HTTP reference. HTTP/1.1, HTTP/2, HTTP/3, caching headers, CORS, cookies, status codes, and connection management.

The standard for web application security. SQL injection, XSS, CSRF, broken authentication — know all 10 with mitigations for security-focused interviews.

Classic free guide to TCP/IP socket programming in C. Deep understanding of how TCP connections, UDP, and network I/O actually work.

Excellent articles on DNS, CDN, DDoS protection, TLS/SSL, HTTP/3, and QUIC. Free, well-written, and consistently updated.

Free peer-to-peer mock interviews for coding, system design, and behavioral. Practice being both interviewer and interviewee. Highly recommended.

Anonymous mock interviews with real engineers from top companies. Paid, but free practice interviews available. Great for final prep.

Free collaborative whiteboard for system design interviews. Practice drawing architectures. Many companies use this or similar tools during virtual interviews.

Common platform for company assessments. Practice SQL challenges, regex, and role-specific tracks. Many companies send HackerRank OAs.

Identifies the 16 core patterns behind coding interview problems: sliding window, two pointers, fast/slow pointer, merge intervals, and more.

Comprehensive end-to-end guide: resume, behavioral questions, coding, system design, and salary negotiation. Free and open source.