Parking Lot

# Design a parking lot system
#
# Requirements:
# - A parking lot has spots of different sizes: small, medium, large
# - Small spots fit small vehicles only
# - Medium spots fit small or medium vehicles
# - Large spots fit any vehicle
#
# Your system should support:
# - Creating a lot from a list of (spot_id, size) tuples
# - Parking a vehicle (returns spot_id or None)
# - Removing a vehicle (returns True/False)
# - Counting available spots
#
# Example:
#   lot = ParkingLot([("S1", "small"), ("M1", "medium")])
#   lot.park_vehicle("car1", "small")  # returns "S1"
#   lot.get_available_spots()           # returns 1