Design a Parking Lot | Machine Coding Round Questions (SDE I/II)

Machine Coding Round Complete Guide

What is a Machine Coding Round?

How to prepare for Machine Coding Round?

How to clear the Machine Coding Round?

Machine Coding Round Interview Practice Questions

Machine Coding Round Interview Solutions/Editorials

Problem Statement

A parking lot is an area where cars can be parked for a certain amount of time. A parking lot can have multiple floors with each floor having a different number of slots and each slot being suitable for different types of vehicles.

Source: https://commons.wikimedia.org/wiki/File:P3030027ParkingLot_wb.jpg

For this problem, we have to design the next generation parking lot system which can manage a parking lot without any human intervention.

Requirements

Create a command-line application for the parking lot system with the following requirements.

The functions that the parking lot system can do:

Create the parking lot.
Add floors to the parking lot.
Add a parking lot slot to any of the floors.
Given a vehicle, it finds the first available slot, books it, creates a ticket, parks the vehicle, and finally returns the ticket.
Unparks a vehicle given the ticket id.
Displays the number of free slots per floor for a specific vehicle type.
Displays all the free slots per floor for a specific vehicle type.
Displays all the occupied slots per floor for a specific vehicle type.

Details about the Vehicles:

Every vehicle will have a type, registration number, and color.
Different Types of Vehicles:

Car
Bike
Truck

Details about the Parking Slots:

Each type of slot can park a specific type of vehicle.
No other vehicle should be allowed by the system.
Finding the first available slot should be based on:

The slot should be of the same type as the vehicle.
The slot should be on the lowest possible floor in the parking lot.
The slot should have the lowest possible slot number on the floor.

Numbered serially from 1 to n for each floor where n is the number of parking slots on that floor.

Details about the Parking Lot Floors:

Numbered serially from 1 to n where n is the number of floors.
Might contain one or more parking lot slots of different types.
We will assume that the first slot on each floor will be for a truck, the next 2 for bikes, and all the other slots for cars.

Details about the Tickets:

The ticket id would be of the following format:
<parking_lot_id>_<floor_no>_<slot_no>
Example: PR1234_2_5 (denotes 5th slot of 2nd floor of parking lot PR1234)

We can assume that there will only be 1 parking lot. The ID of that parking lot is PR1234.

Input/Output Format

The code should strictly follow the input/output format and will be tested with provided test cases.

Input Format

Multiple lines with each line containing a command.

Possible commands:

create_parking_lot <parking_lot_id> <no_of_floors> <no_of_slots_per_floor>
park_vehicle <vehicle_type> <reg_no> <color>
unpark_vehicle <ticket_id>
display <display_type> <vehicle_type>

Possible values of display_type: free_count, free_slots, occupied_slots

exit

Stop taking the input when you encounter the word exit.

Output Format

Print output based on the specific commands as mentioned below.

create_parking_lot

Created parking lot with <no_of_floors> floors and <no_of_slots_per_floor> slots per floor

park_vehicle

Parked vehicle. Ticket ID: <ticket_id>
Print "Parking Lot Full" if slot is not available for that vehicle type.

unpark_vehicle

Unparked vehicle with Registration Number: <reg_no> and Color: <color>
Print "Invalid Ticket" if ticket is invalid or parking slot is not occupied.

display free_count <vehicle_type>

No. of free slots for <vehicle_type> on Floor <floor_no>: <no_of_free_slots>
The above will be printed for each floor.

display free_slots <vehicle_type>

Free slots for <vehicle_type> on Floor <floor_no>: <comma_separated_values_of_slot_nos>
The above will be printed for each floor.

display occupied_slots <vehicle_type>

Occupied slots for <vehicle_type> on Floor <floor_no>: <comma_separated_values_of_slot_nos>
The above will be printed for each floor.

Examples

Sample Input

create_parking_lot PR1234 2 6
display free_count CAR
display free_count BIKE
display free_count TRUCK
display free_slots CAR
display free_slots BIKE
display free_slots TRUCK
display occupied_slots CAR
display occupied_slots BIKE
display occupied_slots TRUCK
park_vehicle CAR KA-01-DB-1234 black
park_vehicle CAR KA-02-CB-1334 red
park_vehicle CAR KA-01-DB-1133 black
park_vehicle CAR KA-05-HJ-8432 white
park_vehicle CAR WB-45-HO-9032 white
park_vehicle CAR KA-01-DF-8230 black
park_vehicle CAR KA-21-HS-2347 red
display free_count CAR
display free_count BIKE
display free_count TRUCK
unpark_vehicle PR1234_2_5
unpark_vehicle PR1234_2_5
unpark_vehicle PR1234_2_7
display free_count CAR
display free_count BIKE
display free_count TRUCK
display free_slots CAR
display free_slots BIKE
display free_slots TRUCK
display occupied_slots CAR
display occupied_slots BIKE
display occupied_slots TRUCK
park_vehicle BIKE KA-01-DB-1541 black
park_vehicle TRUCK KA-32-SJ-5389 orange
park_vehicle TRUCK KL-54-DN-4582 green
park_vehicle TRUCK KL-12-HF-4542 green
display free_count CAR
display free_count BIKE
display free_count TRUCK
display free_slots CAR
display free_slots BIKE
display free_slots TRUCK
display occupied_slots CAR
display occupied_slots BIKE
display occupied_slots TRUCK
exit

Expected Output

Created parking lot with 2 floors and 6 slots per floor
No. of free slots for CAR on Floor 1: 3
No. of free slots for CAR on Floor 2: 3
No. of free slots for BIKE on Floor 1: 2
No. of free slots for BIKE on Floor 2: 2
No. of free slots for TRUCK on Floor 1: 1
No. of free slots for TRUCK on Floor 2: 1
Free slots for CAR on Floor 1: 4,5,6
Free slots for CAR on Floor 2: 4,5,6
Free slots for BIKE on Floor 1: 2,3
Free slots for BIKE on Floor 2: 2,3
Free slots for TRUCK on Floor 1: 1
Free slots for TRUCK on Floor 2: 1
Occupied slots for CAR on Floor 1: 
Occupied slots for CAR on Floor 2: 
Occupied slots for BIKE on Floor 1: 
Occupied slots for BIKE on Floor 2: 
Occupied slots for TRUCK on Floor 1: 
Occupied slots for TRUCK on Floor 2: 
Parked vehicle. Ticket ID: PR1234_1_4
Parked vehicle. Ticket ID: PR1234_1_5
Parked vehicle. Ticket ID: PR1234_1_6
Parked vehicle. Ticket ID: PR1234_2_4
Parked vehicle. Ticket ID: PR1234_2_5
Parked vehicle. Ticket ID: PR1234_2_6
Parking Lot Full
No. of free slots for CAR on Floor 1: 0
No. of free slots for CAR on Floor 2: 0
No. of free slots for BIKE on Floor 1: 2
No. of free slots for BIKE on Floor 2: 2
No. of free slots for TRUCK on Floor 1: 1
No. of free slots for TRUCK on Floor 2: 1
Unparked vehicle with Registration Number: WB-45-HO-9032 and Color: white
Invalid Ticket
Invalid Ticket
No. of free slots for CAR on Floor 1: 0
No. of free slots for CAR on Floor 2: 1
No. of free slots for BIKE on Floor 1: 2
No. of free slots for BIKE on Floor 2: 2
No. of free slots for TRUCK on Floor 1: 1
No. of free slots for TRUCK on Floor 2: 1
Free slots for CAR on Floor 1: 
Free slots for CAR on Floor 2: 5
Free slots for BIKE on Floor 1: 2,3
Free slots for BIKE on Floor 2: 2,3
Free slots for TRUCK on Floor 1: 1
Free slots for TRUCK on Floor 2: 1
Occupied slots for CAR on Floor 1: 4,5,6
Occupied slots for CAR on Floor 2: 4,6
Occupied slots for BIKE on Floor 1: 
Occupied slots for BIKE on Floor 2: 
Occupied slots for TRUCK on Floor 1: 
Occupied slots for TRUCK on Floor 2: 
Parked vehicle. Ticket ID: PR1234_1_2
Parked vehicle. Ticket ID: PR1234_1_1
Parked vehicle. Ticket ID: PR1234_2_1
Parking Lot Full
No. of free slots for CAR on Floor 1: 0
No. of free slots for CAR on Floor 2: 1
No. of free slots for BIKE on Floor 1: 1
No. of free slots for BIKE on Floor 2: 2
No. of free slots for TRUCK on Floor 1: 0
No. of free slots for TRUCK on Floor 2: 0
Free slots for CAR on Floor 1: 
Free slots for CAR on Floor 2: 5
Free slots for BIKE on Floor 1: 3
Free slots for BIKE on Floor 2: 2,3
Free slots for TRUCK on Floor 1: 
Free slots for TRUCK on Floor 2: 
Occupied slots for CAR on Floor 1: 4,5,6
Occupied slots for CAR on Floor 2: 4,6
Occupied slots for BIKE on Floor 1: 2
Occupied slots for BIKE on Floor 2: 
Occupied slots for TRUCK on Floor 1: 1
Occupied slots for TRUCK on Floor 2: 1

Expectations

Make sure that you have a working and demonstrable code
Make sure that the code is functionally correct
Code should be modular and readable
Separation of concern should be addressed
Please do not write everything in a single file (if not coding in C/C++)
Code should easily accommodate new requirements and minimal changes
There should be a main method from where the code could be easily testable
[Optional] Write unit tests, if possible
No need to create a GUI

Optional Requirements

Please do these only if you’ve time left. You can write your code such that these could be accommodated without changing your code much.

Keep the code extensible to add additional types of vehicles and slot types.
Keep the code extensible to allow a different strategy of finding the first available slot.
Keep the code extensible to allow any other type of command.
Keep the code extensible to allow multiple parking lots. You can assume that the input/output format can be changed for that.
Keep the system thread-safe to allow concurrent requests.