Parking Lot

medium · classes + state, allocation

Brief-reported interview attribution (unverified): Amazon, Microsoft, Uber, Google

Design a parking lot with several floors. Each floor has spots of three sizes: compact, regular, large. Vehicles are bike, car, truck. A bike fits any spot, a car fits regular or large, a truck fits large only. Parking takes the first fitting free spot in floor order, then spot order. A ticket records vehicle type, floor, spot, and entry time. Fees are per hour: bike $1, car $2, truck $4. Timestamps are integers (hours) passed by the caller.

class ParkingLot:
    def __init__(self, floors):
        # floors: list of dicts, e.g. [{"compact": 2, "regular": 2, "large": 1}]
    def park(self, vehicle_type, timestamp):
        # -> ticket id (int, starting at 1), or None if no fitting spot / bad type
    def unpark(self, ticket_id, timestamp):
        # -> fee (int) = (timestamp - entry) * rate, or None if the ticket is unknown/used
    def free_spots(self, floor, vehicle_type):
        # -> number of free spots on that floor that fit the vehicle (0 for a bad floor/type)

Rules. A vehicle that does not fit anywhere returns None from park. unpark with an unknown or already-used ticket returns None and changes nothing. A car must not take a compact spot while a regular one is free.

Money units: fees are whole dollars, not cents; a three-hour car stay returns 6.

Tests use explicit inputs and injected clocks/callbacks. No network, real threads or application-server execution is involved.

Public demo

# Public demo: run after implementing the class API above.
p = ParkingLot([{'compact': 1, 'regular': 1, 'large': 1}, {'compact': 0, 'regular': 1, 'large': 0}])
print(p.park('bike', 0))

Starter code

class ParkingLot:

    def __init__(self, floors):
        """floors: list of dicts, e.g. [{"compact": 2, "regular": 2, "large": 1}]"""
        pass

    def park(self, vehicle_type, timestamp):
        """-> ticket id (int, starting at 1), or None if no fitting spot / bad type"""
        pass

    def unpark(self, ticket_id, timestamp):
        """-> fee (int) = (timestamp - entry) * rate, or None if the ticket is unknown/used"""
        pass

    def free_spots(self, floor, vehicle_type):
        """-> number of free spots on that floor that fit the vehicle (0 for a bad floor/type)"""
        pass

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