Low Level Design

Low Level Design foundations — programming paradigms, the four OOP pillars, object relationships, UML diagrams, SOLID and the principles beyond it, domain modeling, refactoring bad designs, layered architecture & dependency injection, and the 4-step LLD interview framework.

All 22 Gang-of-Four design patterns — Creational, Structural and Behavioral — each with intent, structure, real code and when-to-use guidance, plus decision trees and a complete quick-reference cheat sheet.

Concurrency and multithreading for Low Level Design interviews — threads, locks, synchronization primitives, race conditions, deadlock, plus the concurrency patterns (thread pool, producer-consumer, reader-writer) that machine-coding rounds actually ask for.

34 real-world Low Level Design problems — Parking Lot, Elevator, Chess, Uber, Amazon, Spotify, and more. Each with UML diagrams, code implementations in Python & Java, design patterns applied, and testing strategies.