Coming soon · System Design

The LLD
Blueprint.

The round where you design classes, not clusters. Learn to turn a vague prompt like "design a parking lot" into clean, extensible, working code in 60–90 minutes, and to explain every choice while you do it.

Class & sequence diagrams
SOLID with real code
Patterns in context
Thread-safe designs
Step-by-step solutions

Planned contents

What it will cover.

The working outline. Chapters may be added or merged as the book is written and reviewed.

What interviewers grade in an LLD round
A repeatable method: clarify, model, interface, code, extend
OOP that matters: encapsulation, composition over inheritance
SOLID, shown with code that breaks and code that bends
UML-lite: class and sequence diagrams you can draw in two minutes

Creational: Factory, Builder, and why Singleton is a trap
Structural: Adapter, Decorator, Facade, Proxy, Composite
Behavioural: Strategy, Observer, State, Command, Chain of Responsibility
Choosing a pattern, and when to use none

Threads, locks and thread-safe classes
Producer-consumer, worker pools and blocking queues
Avoiding deadlocks and race conditions in interview code

Parking lot
Elevator system
Splitwise-style expense sharing
Movie ticket booking
LRU and LFU caches
Rate limiter
Vending machine and ATM
Chess, Snake & Ladder and Tic-tac-toe
Pub-sub message queue
Text editor with undo/redo
Meeting-room scheduler
Food-delivery order flow

Pattern cheat sheet
The extension questions interviewers ask next
A self-review checklist for your code

Who it's for

Written for you if…

Preparing for SDE-1 / SDE-2

Many product companies run a dedicated LLD or machine-coding round. This is the book for it.

Strong at DSA, unsure about design

You can solve problems but your code gets messy when requirements change. Learn to structure it.

Working engineers

Patterns and principles explained through real trade-offs, not textbook definitions.

FAQ

Questions, answered.

How is this different from the HLD Blueprint?

HLD is about architecture: services, databases, caches and scale. LLD is about the code inside one service: classes, interfaces, patterns and correctness. Most interview loops test both, in separate rounds.

Which programming language will it use?

The designs are language-neutral, with code in a mainstream object-oriented language. The ideas carry over directly to Java, C++, Python, C# or TypeScript.

When will it be out?

It is being written now, to the same standard as the HLD book. We will not announce a date until it is finished and reviewed. Join the waitlist and you will get one email the day it launches.

What will it cost?

Pricing will be announced at launch. Waitlist members get launch pricing.

More Blueprints