Low-Level Design for MAANG Interviews

A book-shaped table of contents for LLD interview prep: OOP fundamentals through SOLID, design principles, UML, design patterns, dependency management, reliability, concurrency, domain modeling, API design, testing, refactoring, classic interview problems, advanced architecture, and performance — cross-linking Object-Oriented Programming and Patterns instead of duplicating them.

1 — Parking Lot

Models a multi-level parking lot with heterogeneous vehicle and spot types, exercising strategy-based spot allocation and a clean split between lot, floor, and spot entities.

10 — ATM

Models an ATM's cash withdrawal, deposit, and balance-inquiry flows, exercising the state pattern across card-inserted, PIN-entry, and transaction states plus the greedy cash-dispensing algorithm.

11 — Vending Machine

Models a vending machine's product inventory, coin/payment handling, and dispensing logic, exercising the state pattern across idle, selection, payment, and dispense states.

12 — Coffee Machine

Models a coffee machine with multiple beverage recipes and shared ingredient inventories, exercising the recipe/ingredient composition model and low-stock/refill handling.