krishankantray/subtraction-on-go

Tech Stack used :

Node.js
Express
Sequelize
MySQL

Project setup via Docker

First goto project root directory.

Then run below commands :

sudo docker build -t subtraction-on-go .

sudo docker run -p 9000:9000 subtraction-on-go

Project setup without docker

Install all dependencies

npm install

Run test cases

npm test

Start local development server

npm start

This app is also deployed on - https://subtraction-on-go.herokuapp.com/

There are three endpoints available :

Generate without save :

curl --location --request GET 'https://subtraction-on-go.herokuapp.com/api/generateQuestionWithoutSaving' \
--header 'Content-Type: application/json' \
--data-raw '{
  "totalQuestions" : 10,
  "minuendDigits" : 5,
  "subtrahendDigits" : 4,
  "isBorrow" : false
}'

Generate and save :

curl --location --request POST 'https://subtraction-on-go.herokuapp.com/api/generateQuestionAndSave' \
--header 'Content-Type: application/json' \
--data-raw '{
  "totalQuestions" : 1,
  "minuendDigits" : 5,
  "subtrahendDigits" : 4,
  "isBorrow" : false
}'

Get all questions :

curl --location --request GET 'https://subtraction-on-go.herokuapp.com/api/getAllQuestions' \
--header 'Content-Type: application/json' \
--data-raw ''

Database Structure

The database contains only one table called - questions

Below is the structure of the table :

All bonus points covered :

✅ Writing test cases : Test case written using mocha and chai ( app/test )
✅ Dockerfile added
✅ options are of same length as correct answer
✅ Code deployed on Heroku : https://subtraction-on-go.herokuapp.com/

Deatiled discussion of theory of questions and options generation :

All the logics are written inside file : app/helpers/subtractionGenerator.js

Question Generation logic

We handle borrow and no borrow conditions separately.

For case when borrow is needed :
When borrow is needed then we just generate two random number of given length utill alteast one borrow is there in the question. Sudo Code :
```
do{
    // generate two random numbers of given length
} while( ! isBorrowExist)
```
For case when borrow is not needed :
This was really tricky to implement 🥵

When borrow is not needed then we generate the minuend randomly of given length with a condition that the digit at subtrahendDigits of minuend number should not be 0 .

For generating subtrahend, we follow minuend digit by digit and generate random digit less than the minuend .

Options generation logic

For generating the options, we find the number of digits in the difference (minuend - subtrahend) , then generate ramdom number having same number of digits as that of difference.

And we shuffle the options[] array using below logic :

options.sort( () => .5 - Math.random() );

The sort() function takes a comaparator, in this case, the comparator sometimes returns positive and somtimes negative.

krishankantray / subtraction-on-go