Post by Aditya Singh Sisodiya

I failed my first LLD interview in 2021. The question was "Design a Parking Lot." I knew OOP. I knew classes. But when the interviewer asked me to make pricing extensible, I froze. Then I learned 12 design patterns. Not all 23 from the GoF book. Just the 12 that actually show up in interviews. The Big 4 (cover 80% of questions): → Strategy (different algorithms for same task) → Observer (notify when something changes) → Factory (create objects based on type) → State (behavior changes with status) Plus 8 more: Singleton, Decorator, Builder, Adapter, Command, Iterator, Template Method, Chain of Responsibility. Each pattern mapped to the exact interview question where it appears. Full article with code examples for all 12 : Link in comments. #designpatterns #lld #softwareengineer #interviews