Problem

League Backend Challenge

In main.go you will find a basic web server written in GoLang. It accepts a single request /echo. Extend the webservice with the ability to perform the following operations

Given an uploaded csv file

1,2,3
4,5,6
7,8,9

1. Echo (given)

   • Return the matrix as a string in matrix format.

   // Expected output
   1,2,3
   4,5,6
   7,8,9
   

2. Invert

   • Return the matrix as a string in matrix format where the columns and rows are inverted

   // Expected output
   1,4,7
   2,5,8
   3,6,9
   

3. Flatten

   • Return the matrix as a 1 line string, with values separated by commas.

   // Expected output
   1,2,3,4,5,6,7,8,9
   

4. Sum

   • Return the sum of the integers in the matrix

   // Expected output
   45
   

5. Multiply

   • Return the product of the integers in the matrix

   // Expected output
   362880
   

The input file to these functions is a matrix, of any dimension where the number of rows are equal to the number of columns (square). Each value is an integer, and there is no header row. matrix.csv is example valid input.

Run web server

go run .

Send request

curl -F 'file=@/path/matrix.csv' "localhost:8080/echo"

What we're looking for

• The solution runs
• The solution performs all cases correctly
• The code is easy to read
• The code is reasonably documented
• The code is tested
• The code is robust and handles invalid input and provides helpful error messages

install tools

install maven >>

https://maven.apache.org/install.html

install Java8

https://www.java.com/es/download/

build and run tests

mvn clean install

if everything is ok. run it like

mvn spring-boot:run

Calling the services

curl -i -X POST -H "Content-Type:multipart/form-data" -F "csv=@\"./matrix.csv\";type=text/csv;filename=\"matrix.csv\"" 'http://localhost:8080/echo'

curl -i -X POST -H "Content-Type:multipart/form-data" -F "csv=@\"./matrix.csv\";type=text/csv;filename=\"matrix.csv\"" 'http://localhost:8080/sum'

curl -i -X POST -H "Content-Type:multipart/form-data" -F "csv=@\"./matrix.csv\";type=text/csv;filename=\"matrix.csv\"" 'http://localhost:8080/multiy'

curl -i -X POST -H "Content-Type:multipart/form-data" -F "csv=@\"./matrix.csv\";type=text/csv;filename=\"matrix.csv\"" 'http://localhost:8080/flatten'

curl -i -X POST -H "Content-Type:multipart/form-data" -F "csv=@\"./matrix.csv\";type=text/csv;filename=\"matrix.csv\"" 'http://localhost:8080/inverse'

Structure

the main entrance is the package controller. we have a controller called MatrixController . (front controller pattern by spring) that controller is calling a util class called **Matrixtransformer ** to transform and get a Object Domain Matrix (inside com.league.matrix.domain package) from a csv file , it looks like a parser. and also a validator object to make sure if that object is Valid (in this case if the matrix is a square)

Then I had two possibilities , define all the functions related to the matrix inside the matrix object or for some functions like sum, multiply and flatten I could have defined an interface which defines that behaviour that implement it from a class. But for this easy case and first iteration I've decided to do it like the first way mentioned.

So the core business in this case is all inside the Matrix domain object.

There are junit tests for Validator, Matrix, and parser. to test controllers over Java I should create integration tests.

Other things

I've used java 8 lambda expresions in some cases, but I could have resolved with two fors or one for iterating over the array of array called data inside the matrix

I've used spring boot, in order to make the things easier to run and build the project. log4j for logs and there is an Application class and application.properties in order to initialize beans.

There is no service or dao layers. I though it was not necessary .

Errors

if the matrix if not valid or the file is empty or there is some problem at parser time with the file. the application will return a bad request http verb. but I could have customize exception for every cases. It should be a good practice.