Two structured courses, start to finish
One for system design, one for data structures and algorithms. Both are free, and both link straight into the practice material.
System Design
System design, topic by topic
Every core system design topic broken into short tutorials with diagrams and worked examples. ACID, caching, sharding, queues, rate limiting, and full design walkthroughs like URL shorteners and chat systems.
12 sections61 topics228 tutorials~10 hours
View the syllabusData Structures & Algorithms
DSA fundamentals from zero
A beginner course on data structures and algorithms with Java examples. Big-O, arrays, hash maps, trees, graphs, recursion, and dynamic programming, each lesson linking to techniques you can practice right after.
7 chapters22 lessons~2.3 hours
Start learningDSA cheatsheetEvery pattern as a trigger word and a one-line tell, for the night before an interview.Java cheatsheetCollections, graph and pattern templates, and the tricks that save you time under pressure.All 200 techniquesThe full index by topic and pattern, each with Java, complexity, and the problems that use it.