The parking lot is the interviewer’s favorite LLD warm-up — not because garages are interesting, but because a good design reveals whether you instinctively separate concerns, reach for interfaces, and keep behaviour out of storage classes.
Nail the requirements first
Pin down what “done” means before a single class. The functional/non-functional split is what separates a design that works from one that survives change.
- Vehicle enters → gets a fitting spot → receives a ticket
- Vehicle exits → fee computed → spot freed → ticket closed
- Reject entry when lot is full for that vehicle size
- Spot sizes and level count are configurable
- Allocation strategy is pluggable (nearest, best-fit, …)
- Pricing strategy is pluggable (flat, tiered, surge, …)
- Availability check is O(1) per size — not a full scan
- Adding EV spots or a new level requires no rewrite
The members-only walkthrough picks up from here: a live simulator you can drive cars into and toggle allocation strategies on, the full class model behind a labelled diagram, the O(1) availability trick, the pluggable allocation and pricing strategies with their code in Java, C++, and Python, the codeable interface you implement against, and the interview corner with edge cases and a practice challenge.
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