design pattern - on code level. Factory, GOF
architecture pattern - block level dia. like MVC
architecture style - principles like REST, microservices
There are 23 design patterns, divided into 3 categories:
| Category | Count | Patterns |
|---|---|---|
| Creational | 5 | Singleton, Factory Method, Abstract Factory, Builder, Prototype |
| Structural | 7 | Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy |
| Behavioral | 11 | Chain of Responsibility, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor |
For a senior LLD interview, you don’t need equal depth on all 23. I’d prioritize roughly 10–12:
Must know deeply: Strategy, Decorator, Factory Method, Builder, Observer, State, Adapter, Facade, Command, Chain of Responsibility.
Then understand Singleton, Proxy, Composite, Template Method well enough to recognize and discuss them.
Creational
- Builder
Structural
- Decorator
Behavior
- Strategy