System Design · LLD
Low-Level Design
Machine-coding and OOD interviews: entities, class diagrams, design patterns and clean Java implementations.
01Warm-ups
4
02Physical Systems
4
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How to use this track
Low-level design rounds, also called machine coding or object-oriented design interviews, ask you to model a real system in clean, extensible code. These guides cover common problems such as a parking lot, elevator, vending machine, LRU cache and Splitwise.
Each guide lists the requirements, identifies the core entities and their relationships, shows a class diagram, explains the design patterns used and gives a complete Java implementation you can run and extend.
To practise, read the requirements, then spend 30 minutes designing the classes yourself before comparing with the guide. Focus on clear responsibilities, the SOLID principles and patterns such as Strategy, State, Observer and Factory.
The OOP and LLD cheat sheet summarises the principles and patterns with short Java examples, which makes it a useful warm-up before a machine coding round.