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the five-year mile
Master the HLD, LLD, and CS fundamentals that make or break interviews. Learn through first-principles reasoning and complete, production-ready code.
Understand the why. Don’t just memorize the what.
Dive into full, file-by-file implementations using our integrated IDE viewer. Because the best way to learn is by reading real code.
// SYSTEM DESIGN// Q: Design an API rate limiter —// N requests per window, per client,// O(1) to check and thread-safe. Every article moves you one marker further down the road.
Year 1
Ships features that work
Year 2
Reads big codebases fast
Year 3
Owns a service end to end
Year 4
Designs for scale & failure
Year 5
Reasons from first principles
Fresh from the notebook
A low-level-design walkthrough of an O(1) LRU cache in Java — HashMap plus an intrusive doubly linked list — and how to make it correct under concurrency. Includes the full, browsable implementation.
Dijkstra's algorithm derived from its invariant, with the complexity analysis that explains why a binary heap gives O((V + E) log V) and a clean Java implementation.
How to design a rate limiter — algorithms, trade-offs, and a production-ready, thread-safe token bucket wired into Spring Boot as an interceptor.
Start with the two that interviews lead with