Preview — Pro guide
You are seeing a portion of this guide. Sign in and upgrade to unlock the full article, quizzes, and interview answers.
LLD Case Study: Parking Lot System (Production-Grade)
Deep-dive production design of a multi-floor parking lot with EV charging, dynamic pricing, reservations, and concurrent access. Goes beyond basic OOP to cover lock granularity, optimistic concurrency, and real extension patterns interviewers probe at senior level.
What This File Is NOT
The lld-framework.yaml file already introduces parking lot as a 5-step walkthrough example with the basic class diagram and core implementation. This deep-dive assumes you've seen that — it covers production complexity: multi-floor layouts, EV charging bays, advance reservations, and the concurrency trap that fails 70% of senior candidates. If you haven't read the framework file first, do that now.
Why Parking Lot Is the Canonical LLD Interview Problem
Parking lot appears in more FAANG LLD interviews than any other problem — not because it's intrinsically interesting, but because it is a scope-controlled vehicle for testing every dimension of OOP design simultaneously: entity modeling, inheritance vs composition, design patterns, concurrency, and extensibility. A candidate who handles parking lot well almost certainly handles more complex real-world LLD problems well.
The critical insight most candidates miss: the interviewer is not evaluating whether you can build a parking lot. They are using parking lot to probe:
- Can you distinguish between domain entities (what the system is) and service objects (what the system does)?
- Do you apply design patterns because they solve real problems, or because you memorized names?
- At what level of granularity do you apply locking, and can you reason about the tradeoffs?
- How do you add requirements (reservations, EV, pricing tiers) without rewriting core classes?
Candidates who treat parking lot as a data-modeling exercise — just defining ParkingSpot with fields — produce designs that collapse under the first extension request. The goal is a design where adding a new vehicle type, a new pricing model, or a new spot category requires adding a class, not editing existing ones.