This repository is an educational resource focused on teaching low-level design (LLD) and object-oriented design (OOD) principles through runnable code examples. It contains implementations of the Gang of Four design patterns (creational, structural, behavioral) across multiple programming languages including C++, Java, C#, Python, Go, and JavaScript/TypeScript. Additionally, it provides problem statements and solutions for common LLD interview questions such as parking lot systems, ATM implementations, vending machines, and social networking platforms. The repository serves as both a reference guide and a practical learning tool. Each design pattern is demonstrated with minimal, focused examples that isolate the pattern's core mechanics. The problem/solution sections show how these patterns can be applied in real-world scenarios, complete with class diagrams and explanations. While the code is functional and demonstrative, it prioritizes clarity of concept over production robustness, making it ideal for learning but requiring adaptation for actual deployment. Although primarily educational, the repository contains executable code that could be considered a collection of mini-applications. Each pattern implementation and problem solution can be run independently to observe the behavior. The multi-language approach allows developers to compare how the same pattern is expressed in different ecosystems, highlighting both universal principles and language-specific idioms.
This repository is a curated collection of low-level design (LLD) and machine coding round solutions, primarily targeting interview preparation. It contains over 15 self-contained subprojects, each modeling a classic system design problem such as chess, elevator control, Uber ride booking, Splitwise expense splitting, parking lot, stock broker, task scheduler, Kafka message queue, in-memory key-value store, and more. Each subproject follows a consistent architecture with domain models, repository interfaces with in-memory implementations, service classes, and often a Main or Demo class for standalone execution. The code heavily employs design patterns like Strategy, Factory, Repository, and Observer, and demonstrates concurrency handling with locks, atomic variables, and thread-safe collections. The collection is not intended for production deployment; all state is volatile and stored in-memory. While the quality is uneven across subprojects, many exhibit clean separation of concerns and extensible design. The repository serves as a practical study resource for object-oriented design, with problem statements and video tutorials linked in the README. Some subprojects have multiple iterations (e.g., Kafka from simple to production-grade) showing evolution, but this also introduces duplication and occasional inconsistencies in naming and package structure. Despite the lack of automated tests and incomplete implementations in a few areas, the overall codebase demonstrates solid craftsmanship for educational purposes. A handful of modules—such as the distributed cache with consistent hashing, the circuit breaker for resilience, the order matching engine, and the heap-based feed fetch strategy—are particularly well-isolated and could be extracted for reuse in other projects with minimal adaptation.