SOLID_Principles.cpp

SOLID Principles: For every major class, state which SOLID principles it adheres to. (e.g., "I'm making ParkingFeeCalculator an interface to follow OCP and DIP.")

Trade-offs: If a design choice is made (e.g., using a Strategy Pattern), explicitly mention the trade-off (e.g., "The trade-off is slightly higher code complexity due to more interfaces, but vastly improved maintainability and extensibility.").

Encapsulation/Abstraction: Define the clear public interfaces (APIs) and hide implementation details.

UML: Use simple, clear boxes and arrows to show the relationships (Association, Inheritance, Composition).



🛠️ Core Principles & Patterns to Showcase
For Principal Engineer and similar senior roles, your discussion should go beyond just drawing a class diagram. You must justify your design choices 
using core software engineering principles:

SOLID Principles: Be ready to articulate exactly how each principle applies to your design.

Single Responsibility Principle (SRP): Each class/module should have only one reason to change (e.g., Booking class handles bookings, not payments).

Open-Closed Principle (OCP): Software entities should be open for extension but closed for modification 
  (e.g., adding a new vehicle type in a parking lot should not require modifying the core ParkingLot class).

Liskov Substitution Principle (LSP): Subtypes must be substitutable for their base types 
  (e.g., all vehicle types can be parked by the same ParkingLot methods).

Interface Segregation Principle (ISP): 
  Clients should not be forced to depend on interfaces they do not use (e.g., separate interfaces for Admin vs. User functions).

Dependency Inversion Principle (DIP): 
  Depend on abstractions, not concrete implementations (e.g., the VendingMachine depends on a PaymentProcessor interface, not a concrete CreditCardProcessor class).


  
Design Patterns: 
  Be able to use and name appropriate GoF Design Patterns to solve specific problems. Common ones include Factory, Singleton, Strategy, Observer, State, and Decorator.

  
Concurrency: 
  Discuss thread safety, locking mechanisms, and handling concurrent access to shared resources (e.g., simultaneous bookings for a seat, concurrent updates to a cache).

  
💡 Principal Engineer Differentiation
For a Principal Engineer, the expectations are much higher than for a general Software Development Engineer:

Trade-off Analysis: Deeply analyze trade-offs between different design choices (e.g., using an array vs. a hash map + doubly linked list for LRU cache, 
  or choosing a specific database/cache for a component).

Scalability & Reliability at LLD: 
  Discuss how your LLD approach makes the component easier to scale and more reliable within the context of the larger system. For instance, 
  designing a thread-safe cache or using the Factory Pattern to make components easily swappable (e.g., different payment gateways).

Extensibility (OCP focus): 
  Provide examples of how your design is easily extensible for future requirements without changing core code 
    (e.g., "If we add a new premium parking spot type, we only need to add a new class that extends ParkingSpot").

Integration Points: Explicitly define the APIs/interfaces of your LLD component that the High-Level Design (HLD) services would consume.

The video below explains how to master Low-Level Design interviews using free resources, which is a great starting point for tackling these problems.

How I Mastered Low Level Design Interviews is a resource that shares tips on mastering Low-Level Design interviews.