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Hectal
Roadmap
Phase 1Beginner3 of 19 in the curriculum

OOP + SOLID + UML

The vocabulary every LLD answer is graded on.

LLD interviews are, at heart, OOP interviews. Before you design a parking lot you must be able to explain why inheritance can be a trap, what an interface is actually for, and which SOLID letter is violated by the code you just saw.

Do not memorize definitions. For each principle, ask: what production problem does this prevent?

0/5 · 0%
5 topics ~44 min 5 code blocks & diagrams
Start with the first topic
1
1.1

OOP

Four pillars (encapsulation, inheritance, polymorphism, abstraction) plus the relationship vocabulary (composition, aggregation, association, dependency) that LLD answers are built from.

7 min 1 code practice

2
1.2

SOLID

Five principles that keep a codebase changeable: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion. For interviews, connect each to the production pain it prevents.

9 min 2 code practice

3
1.3

UML / Class Relationships

Interviews rarely ask you to draw formal UML, but the relationship vocabulary (1:1, 1:N, N:N, association, aggregation, composition, inheritance, dependency) is used constantly to describe a class diagram out loud.

6 min practice

4
1.4

Abstraction Design

Choosing the right abstraction — interface vs abstract class vs concrete class — and the two patterns that power most LLD answers (strategy and factory).

7 min 1 code practice

5
1.5

Domain Modeling Essentials

Entities, value objects, invariants, immutability, and a deliberate error model. Most LLD bugs come from anemic data bags that let invalid state exist, not from missing patterns.

15 min 1 code practice