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Hectal
Roadmap
Phase 3Intermediate5 of 19 in the curriculum

LLD Foundations

The repeatable method behind every LLD answer.

Before solving any problem, learn the extraction method. Given a vague problem statement ('design a parking lot'), there is a systematic way to produce requirements, entities, responsibilities, and extensions — and it works for every problem in Phase 4.

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7 topics ~56 min 6 code blocks & diagrams
Start with the first topic
1
3.1

Requirement Analysis

Given a problem like Parking Lot, you must enumerate the actors, objects, rules, and edge cases before any code — this is the difference between a designer and a coder in an interview.

8 min 1 code practice

2
3.2

Identify Entities

Nouns become entities, verbs become operations, rules become business logic. A disciplined translation from English to classes.

7 min 1 code practice

3
3.3

Responsibility Assignment

The single most important LLD skill: deciding which class owns which behavior — and keeping responsibilities from bleeding across classes.

6 min practice

4
3.4

Extensibility

Design so a new variation — payment method, vehicle type, pricing rule, storage, channel — does not rewrite the system.

7 min 1 code practice

5
3.5

Dependency Injection

The binding that holds LLD designs together: interface → implementation → constructor injection → Spring bean. It is the mechanism that makes strategy, port/adapter, and testability real.

7 min 1 code practice

6
3.6

Testing Your LLD

A design is only proven when tests show it works and stays easy to change. A few sharp unit tests for the rules and edge cases are what separate 'it compiles' from 'I'd ship this'.

13 min 1 code practice

7
3.7

The LLD Interview, Start to Finish

Put Phases 1–3 together into one repeatable 45-minute script: requirements → entities → class diagram → core code → concurrency → extensions. Use it for every problem in Phase 4.

8 min 1 code practice