LLD - Low Level Design Practice

This repository is for Low Level Design (LLD) and design pattern practice in Java.

HLD topics should be kept in a separate repository. This repo should focus only on class design, object relationships, design patterns, UML, and machine-coding style problems.

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Design Patterns Checklist

Use this section to quickly know which design patterns are already covered in this repository and which ones still need to be added.

Done	Design Pattern	Folder / Example	Main Use
[x]	Factory Pattern	FactoryPattern, Parking_System, Bookmyshow	Create objects based on type without exposing creation logic
[x]	Singleton Pattern	Singleton, Bookmyshow, uber-ride-system	Keep only one shared instance of a service/manager
[x]	Strategy Pattern	StrategyPattern, Parking_System, uber-ride-system	Change algorithm/behavior at runtime
[x]	Observer Pattern	ObserverPattern	Notify subscribers when something changes
[x]	Decorator Pattern	DecoratorPattern	Add extra behavior dynamically
[x]	Proxy Pattern	ProxyPattern	Control access to a real object
[x]	Adapter Pattern	Structural_Pattern/AdapterPattern	Make incompatible interfaces work together
[x]	Chain of Responsibility	ChainofResponsibility, LogProcessor	Pass request through a chain of handlers
[x]	State Pattern	Behavioural_Pattern/StatePattern	Change object behavior based on state
[x]	Null Object Pattern	LLDofNULLobject	Avoid null checks using default object behavior
[x]	Builder Pattern	Creational_Pattern/BuilderPattern	Build complex objects step by step
[ ]	Composite Pattern	Pending	File system, menu tree, organization hierarchy
[ ]	Command Pattern	Pending	Undo/redo, remote control, task execution
[ ]	Template Method Pattern	Pending	Fixed algorithm structure with customizable steps
[ ]	Facade Pattern	Pending	Simple interface over a complex subsystem
[ ]	Iterator Pattern	Pending	Traverse collections without exposing internals
[ ]	Mediator Pattern	Pending	Reduce direct dependency between many objects

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LLD Problems Checklist

Use this section to track which LLD interview problems are already covered and which ones still need to be implemented.

Done	LLD Problem	Folder / Status	Main Concepts
[x]	BookMyShow	Bookmyshow	Movie, theatre, show, screen, seats, booking flow
[x]	Parking Lot	Parking_System	Vehicle, spot, floor, gate, ticket, payment
[x]	Uber / Ride Sharing	uber-ride-system	Rider, driver, ride, fare, matching
[x]	Logger System	LogProcessor	Log levels, chain of responsibility
[x]	Custom HashMap	HashMap_Internal_Implementation	Hashing, bucket, collision handling
[x]	Notification System	ObserverPattern	Subscribers, notification strategies
[x]	Order State Flow	Behavioural_Pattern/StatePattern	Order lifecycle using state pattern
[x]	Association Examples	Associations	One-to-one, one-to-many, many-to-many
[ ]	Elevator System	Pending	Elevator states, request scheduling, direction handling
[ ]	Splitwise	Pending	Expense sharing, balances, debt simplification
[ ]	Vending Machine	Pending	State pattern, inventory, payment, dispense flow
[ ]	ATM Machine	Pending	Authentication, cash withdrawal, cash inventory
[ ]	LRU Cache	Pending	HashMap, doubly linked list, eviction
[ ]	Snake and Ladder	Pending	Board, dice, players, game loop
[ ]	Tic Tac Toe	Pending	Board, players, winning strategy
[ ]	Chess	Pending	Piece hierarchy, move validation, board state
[ ]	Library Management System	Pending	Books, members, borrowing, fines
[ ]	Meeting Scheduler	Pending	Calendar, time slots, conflict detection
[ ]	Hotel Booking	Pending	Room inventory, date range availability, booking
[ ]	Food Delivery LLD	Pending	Restaurant, menu, cart, order, delivery partner
[ ]	File System	Pending	Composite pattern, file-directory tree
[ ]	Rate Limiter LLD	Pending	Token bucket, sliding window, request limits
[ ]	Car Rental System	Pending	Vehicle inventory, booking, pricing, payment

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Note

This repository is only for LLD.

Keep these in a separate HLD repository:

• URL Shortener
• WhatsApp / Chat System
• YouTube / Netflix
• Instagram / Twitter Feed
• Uber HLD
• BookMyShow HLD at scale
• Payment System HLD
• Distributed Cache
• Search Autocomplete
• Sharding and replication
• Kafka / message queue systems