Three doors
01OOP
Nouns that own state
02Guidelines
Decide cleanly + STAR
03Patterns
Only when a seam appears
04Delivery
35-minute talk track
This page is a routing card. Don’t re-read it mid-interview — pick the deep dive that matches the gap you’re filling this week.
- OOP & design principles — encapsulation, inheritance vs composition, SOLID instincts for modeling.
- Guidelines, STAR & pattern instincts — KISS / DRY / YAGNI / Demeter, how to narrate, when a basic pattern is earned.
- Design patterns for LLD — Strategy, Factory, Observer, Singleton (carefully), Decorator — with interview timing.
- Delivery framework — the clock: clarify → model → API → implement → extend.
When to open which post
One-week practice path
- Day 1–2 — OOP modeling on Parking or Tic Tac Toe without naming patterns.
- Day 3 — Guidelines pass: cut dead classes; narrate STAR for one API.
- Day 4 — Re-do Rate Limiter and deliberately place Strategy + Factory.
- Day 5 — Observer only where it pays (inventory low-stock or logger sinks).
- Day 6–7 — Full classic under timer; patterns only if the seam appears live.
Related Lattice posts: Classic LLD index · Concurrency map