Designing a Parking Lot Application has been one of the popular questions in many of the companies like Thoughtworks, Gojek, Amazon etc. This question has all the ingredients to test a candidate’s design skills to build a scalable system.
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| Multi Storey Parking Lot Problem Solution |
Problem Statement:
I own a multi-storey parking lot that can hold up to ‘n’ cars at any
given point in time. Each slot is given a number starting at 1
increasing with increasing distance from the entry point in steps of
one. I want to create an automated ticketing system that allows my
customers to use my parking lot without human intervention.
When a car enters my parking lot, I want to have a ticket issued to
the driver. The ticket issuing process includes us documenting the
registration number (number plate) and the colour of the car and
allocating an available parking slot to the car before actually handing
over a ticket to the driver (we assume that our customers are nice
enough to always park in the slots allocated to them).
The customer should be allocated a parking slot which is nearest to the
entry. At the exit the customer returns the ticket which then marks the
slot they were using as being available.
Due to government regulation, the system should provide me with the
ability to find out:
● Registration numbers of all cars of a particular colour.
● Slot number in which a car with a given registration number is
parked.
● Slot numbers of all slots
where a car of a particular colour is parked.
We interact with the system via a simple set of commands which produce a
specific output. The system should allow input in two ways. Just to
clarify, the same code base should support both modes of input:
1) It should provide us with an interactive command prompt based shell
where commands can be typed in.
2) It
should accept a filename as a parameter at the command prompt and read
the commands from that file.
Example: File
To install all dependencies, compile and run tests:
$ bin/setup
To run the code so it accepts input from a file:
$ bin/parking_lot file_inputs.txt
Input (contents of file):
create_parking_lot 6
park KA-01-HH-1234 White
park KA-01-HH-9999 White
park KA-01-BB-0001 Black
park KA-01-HH-7777 Red
park KA-01-HH-2701 Blue
park KA-01-HH-3141 Black
leave 4
status
park KA-01-P-333 White
park DL-12-AA-9999 White
registration_numbers_for_cars_with_colour White
slot_numbers_for_cars_with_colour White
slot_number_for_registration_number KA-01-HH-3141
slot_number_for_registration_number MH-04-AY-1111Output (to
STDOUT):
Created a parking lot with 6 slots
Allocated slot number: 1
Allocated slot number: 2
Allocated slot number: 3
Allocated slot number: 4
Allocated slot number: 5
Allocated slot number: 6
Slot number 4 is free
Slot No. Registration No
Colour
1
KA-01-HH-1234
White
2
KA-01-HH-9999
White
3
KA-01-BB-0001
Black
5
KA-01-HH-2701
Blue
6
KA-01-HH-3141
Black
Allocated slot number: 4
Sorry, parking lot is full
KA-01-HH-1234, KA-01-HH-9999, KA-01-P-333
1, 2, 4
6
Not found
Example: Interactive
To install all dependencies, compile and run tests:
$ bin/setup
To run the program and launch the shell:
$ bin/parking_lot
Assuming a parking lot with 6 slots, the following commands should be
run in
sequence by typing them in at a prompt and should produce output as
described
below the command. Note that exit terminates the process and
returns control to
the shell.
$ create_parking_lot 6
Created a parking lot with 6 slots
$ park KA-01-HH-1234 White
Allocated slot number: 1
$ park KA-01-HH-9999 White
Allocated slot number: 2
$ park KA-01-BB-0001 BlackAllocated slot number: 3
$ park KA-01-HH-7777 Red
Allocated slot number: 4
$ park KA-01-HH-2701 Blue
Allocated slot number: 5
$ park KA-01-HH-3141 Black
Allocated slot number: 6
$ leave 4
Slot number 4 is free
$ status
Slot No.
1
2
3
5
6
Registration No
KA-01-HH-1234
KA-01-HH-9999
KA-01-BB-0001
KA-01-HH-2701
KA-01-HH-3141
Colour
White
White
Black
Blue
Black
$ park KA-01-P-333 White
Allocated slot number: 4
$ park DL-12-AA-9999 White
Sorry, parking lot is full
$ registration_numbers_for_cars_with_colour White
KA-01-HH-1234, KA-01-HH-9999, KA-01-P-333
$ slot_numbers_for_cars_with_colour White
1, 2, 4
$ slot_number_for_registration_number KA-01-HH-3141
6
$ slot_number_for_registration_number MH-04-AY-1111
Not found
$ exit
Link to my github solution is below:
