https://fiveyearsdev.space Deep, beautifully typeset articles on system design (HLD), low-level design (LLD), and the computer-science fundamentals that decide interviews — everything a developer should know by five years. en https://fiveyearsdev.space/articles/designing-a-thread-safe-lru-cache https://fiveyearsdev.space/articles/designing-a-thread-safe-lru-cache Tue, 02 Jun 2026 00:00:00 GMT 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. lld caching concurrency java https://fiveyearsdev.space/articles/dijkstras-shortest-path https://fiveyearsdev.space/articles/dijkstras-shortest-path Thu, 28 May 2026 00:00:00 GMT 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. graphs shortest-path algorithms heaps https://fiveyearsdev.space/articles/designing-a-rate-limiter https://fiveyearsdev.space/articles/designing-a-rate-limiter Wed, 20 May 2026 00:00:00 GMT How to design a rate limiter — algorithms, trade-offs, and a production-ready, thread-safe token bucket wired into Spring Boot as an interceptor. rate-limiting system-design spring-boot concurrency