Parking Lot Problem

See website for information.

Problem Statement

Mr Zorro owns a multi-storey parking lot that can hold up to n vehicles at any given point in time. The parking slots are numbered, beginning at 1 and increases with increasing distance from the entry point in steps of one. Mr Zorro has requested your help to design an automated ticketing system for his parking lot.

When a vehicle enters the parking lot, its vehicle registration number (i.e., number plate) and colour are noted. Then, an available parking slot is allocated. Following are the rules of parking slot ticket issuance:

Each customer should be allocated the nearest available parking slot to the entry point.
Upon exiting the parking lot, the customer returns the ticket which marks their previously allocated lot as now available.
Due to government regulation, the system should provide the ability to determine:
- 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.

The ticketing system should be operable via two modes of input, namely, interactive commands and commands from a file. In other words, the ticketing system should be an executable which accepts:

Interactive commands from an interactive command prompt shell
A filename as an input argument at the command prompt and executes the commands from the given file

Example below includes all the commands which need to be supported.

Example: File Input

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-

Output (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 run the code, launch the shell, and to accept interactive input from the shell:

$ bin/parking_lot

Assuming a parking lot with n=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 Black
Allocated 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. 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
$ 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

Learning Outcome

At the end of this project, we should be able to:

solve the Parking Lot problem with data structures optimized for complexity
write comprehensive unit tests in Golang
perform functional testing in Golang
utilize heap, hash map, and slice, data structures in Go
pretty print slices, arrays, and strings, using an interface

Instructions

Setup Go
- Install Go following the instructions here.
- Set GOROOT which is the location of your Go installation. Assuming it is installed at $HOME/go2.x, execute:
```
export GOROOT=$HOME/go2.x
export PATH=$PATH:$GOROOT/bin
```
- Set GOPATH environment variable which specifies the location of your Go workspace. It defaults to $HOME/go on Unix/Linux.
```
export GOPATH=$HOME/go
```
- Set GOBIN path for generation of binary file when go install is run.
```
export GOBIN=$GOPATH/bin
export PATH=$PATH:$GOPATH/bin
```
Source code
- Git clone the project into $GOPATH/src/parking_lot folder in your computer.
```
git clone https://github.com/Adaickalavan/Parking-Lot-Problem.git $GOPATH/src/parking_lot
```
  Here, git clone syntax follows the pattern: git clone <repo> <local folder-name>.
Executable
- To create an executable in the $GOPATH/bin/ directory, execute
```
go install parking_lot
```
Unit test and functional test
- To run complete test suite, run
```
go test -v parking_lot
```
  Here, -v is the verbose command flag.
- To run specific test, run
```
go test -v parking_lot -run xxx
```
  Here, xxx is the name of test function.
- Test coverage: 94.1% of statements
Running
- Launch interactive user input mode by executing
```
$GOPATH/bin/parking_lot
```
- Launch file input mode by executing
```
$GOPATH/bin/parking_lot.exe $GOPATH/src/parking_lot/inputFile.txt
```
  Here, $GOPATH/src/parking_lot/inputFile.txt refers to the input file with complete path.

Project structure

The project structure is as follows:

project                               # folder containing all project files
├── bin                               # contains executable commands
│   ├── setup                         # place your commands to build/compile the Go code here in `setup` file
│   └── parking_lot.exe               # .exe file for parking_lot generated by `go install` command
└── src                               # contains Go source files
    └── parking_lot                   # main folder
        ├── vendor                    # folder containing dependencies
        │   ├── minheap               # dependant package `minheap`  
        │   │   ├── item.go           # element of heap
        │   │   └── priorityQueue.go  # min heap implementation
        │   └── pretty                # dependant package `pretty`  
        │       └── printer.go        # pretty prints array, slice, string
        ├── car.go                    # element of carpark
        ├── carpark.go                # carpark struct and pointer receiver methods
        ├── carpark_test.go           # unit tests of the carpark.go code
        ├── main.go                   # main file of Go code
        ├── main_test.go              # functional test of the main code
        ├── inputFile.txt             # sample input file for testing
        └── inputInteractive.txt      # sample interactive input for testing

Notes on solution

Data structures
- A hash map and a min heap was used to solve the parking lot problem.
Complexity
- To park a car: O(log(n1)). Here, n1 is the size of the min heap.
- To remove a car: O(log(n1)). Here, n1 is the size of the min heap.
- To retrieve a car by colour: O(n2). Here, n2 is the size of the hash map.
- To retrieve a car by registration number: O(n2). Here, n2 is the size of the hash map.
- To get status: O(n2). Here, n2 is the size of the hash map.
Assumptions and rationale for choice of data structures to optimize complexity
- Car parking and removing operations will be more frequent compared to retrieving car by colour/registration number or status requests.
- A hash map with slot number as key is used to store all the cars parked in the carpark. Complexity O(1) of hash map simplifies insertion and removal of cars by slot number.
- A min heap is used to store previoulsy-occupied-but-now-empty slots in ordered sequence with complexity O(log(n1)) for push and pop operations. Here, empty slots n1 refer only to slots which were previously occupied but is now free. It does not refer to the total number of free slots in the carpark.
Alternative solutions to reduce complexity at the expense of increased memory
- To achieve complexity O(1) in retrieving a car by colour, implement an additional hash map with colour as key to store all the cars parked in the carpark.
- To achieve complexity O(1) in retrieving a car by registration number, implement an additional hash map with registration number as key to store all the cars parked in the carpark.

Adaickalavan / Parking-Lot-Problem