Master the Top Design Patterns for Interviews

Published : 04 June 2025
Updated : 04 June 2025

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Interview System Design Application Design Design Patterns Software Design

If you are preparing for system design or low-level design (LLD) interviews, learning Design Patterns is no longer optional, it’s essential.

In software development, design patterns are proven, reusable solutions to commonly occurring problems in software design. They are not ready-to-run code but general templates that can be applied to solve design challenges in a systematic way.

Originally popularized by the Gang of Four (GoF) in their book “Design Patterns: Elements of Reusable Object-Oriented Software”, these patterns are now essential for building scalable, maintainable, and efficient applications.

They are not code snippets, they are concepts and approaches that guide architecture and class structure.

Why Are Design Patterns Important in Interviews?

Design Patterns often appear in

LLD Rounds (Design a Logger, Pizza Builder, etc.)
System Design Discussions (Scalable Notification System, Payment Gateways)
Project Discussions (Refactoring, SOLID principles)

Interviewers want to see how well you design systems, not just solve algorithms.

Top Design Patterns for Interviews (Categorized by Frequency)

Tier 1: Must-Know Patterns (Frequently Asked)

These patterns show up in 90% of LLD interviews.

Pattern	Type	Use Case Example
Singleton	Creational	Logger, DB connection manager
Factory	Creational	Object creation based on input (Shape Factory)
Builder	Creational	Pizza builder, complex object creation
Strategy	Behavioral	Payment gateway, dynamic pricing
Observer	Behavioral	Notification system, event listeners
Decorator	Structural	I/O streams, adding features to classes
Command	Behavioral	Undo/redo functionality
State	Behavioral	Vending machine, Order processing
Template	Behavioral	Fixed steps with customizable behavior

Tier 2: Good-to-Know Patterns (Occasionally Asked)

These may come up in deeper design questions or senior-level interviews.

Pattern	Type	Use Case Example
Proxy	Structural	Security, logging, lazy-loading
Adapter	Structural	Third-party integrations
Composite	Structural	File system, menu hierarchies
Chain of Responsibility	Behavioral	Request pipelines, validation chains
Mediator	Behavioral	UI components interaction
Abstract Factory	Creational	Creating families of related objects

Tier 3: Advanced Patterns (Rarely Asked Directly)

Not commonly asked, but useful for design discussions and system architecture.

Pattern	Type	Use Case Example
Flyweight	Structural	Game object optimization
Visitor	Behavioral	Performing operations on objects
Memento	Behavioral	Snapshot/undo functionality
Interpreter	Behavioral	Language parsing
Bridge	Structural	Decoupling abstraction/implementation
Prototype	Creational	Object cloning

Basic Format of a Design Pattern

Each design pattern typically includes the following elements

Component	Description
Pattern Name	Name of the pattern (e.g., Singleton, Observer)
Intent	The purpose or goal of the pattern
Problem	What problem it solves in software design
Solution	How the pattern solves the problem
Structure	UML or visual diagram (class relationships)
Participants	The roles/classes involved in the pattern
Code Example	Real or pseudo-code implementation
Consequences	Trade-offs, pros and cons of using the pattern

Real LLD Interview Problems and Matching Patterns

Interview Problem	Design Patterns Used
Design a Logger	Singleton, Factory
Build a Pizza Ordering App	Builder, Decorator
Design a Notification System	Observer, Strategy, Template
Build a Payment Gateway	Strategy, Factory
ATM or Vending Machine	State, Command
Design Middleware/Filters	Chain of Responsibility, Proxy

Final Thoughts

Mastering design patterns helps you stand out in LLD/System Design rounds, they show your thinking, architecture skills and design maturity.

Whether you’re building scalable backend systems or designing object-oriented solutions, design patterns will be your superpower.