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Master Low-Level Design (LLD) and Machine Coding interviews. Deconstruct Creational, Structural, and Behavioral patterns with polymorphic class hierarchies.
The foundation of maintainable, testable, and loosely-coupled object-oriented codebases.
One class, one reason to change
Open for extension, closed for modification
Subtypes must be substitutable for base types
Clients should not depend on unused methods
Depend on abstractions, not concrete classes
The five architectural pillars (SRP, OCP, LSP, ISP, DIP) that transform brittle spaghetti code into flexible, decoupled class hierarchies.
Decoupling object instantiation mechanisms from consuming clients using Factory Method, Abstract Factory, and fluent Builders.
Composing objects into larger structures using Adapters for incompatible interfaces, Decorators for dynamic behavior wrapping, and Facades for simplified APIs.
Managing runtime algorithm switching (Strategy), pub/sub event broadcasting (Observer), and state-dependent class behavior (State).
End-to-end Low-Level Design of a multi-floor Parking Lot and Elevator scheduling system using Clean Architecture and Design Patterns.