carousell-interview-reddit

Reddit clone for Carousell coding challenge

Local Setup

Clone git to local

https://github.com/jomaint/carousell-interview-reddit.git

Install package.json @ backend/frontend folder

npm install

Backend API tests (backend folder)

npm test

Frontend Unit tests (frontend folder)

npm test

Start local server (backend folder)

npm start

Visit frontend web

http://localhost:8000

Front-end

The front-end stack uses the following:

React
Bootstrap
Sass
Gulp

Back-end

The backend stack uses the following:

node.js
Express

Topic data structure

The current topics are stored in memory using two variables:

rank is an array storing the topic id in decreasing order.
topics is a object that uses the topic id as key, storing the topic data as a value.

This way of normalising and storing the topics allows ease of retrieving top 20, simply slicing rank array . Rearrangement of topics during change of vote, we can simply shift, swap, remove any topic without moving the entire data object. We can also access any topic via its id, without having to iterate throught the entire array if we were to store all topics in one variable. Based on the assumption where a topic page is accessed directly, and we have a large number of topics, iterating through an array is not feasible, this data structure would help get a constant access time.

Topic API

Getting list of top 20 Topics

/GET /api/topics

Adding new Topic

/POST /api/topics

key	type
title	string

Upvoting / Downvoting Topic

/PUT /api/topics/:topicId

key	type
newVote	Integer

Each newVote (upvoting/downvoting) is updating the existing vote with the new vote. After which the rearrangement of rank array take place. First locating the index of the target topic in rank. Then check if

the updated vote is smaller than the next topic
the updated vote is larger than the prev topic

If so, run the function recursively to check in the same direction, until we find a final place for the updated topic. This implementation would be far more efficient than iterating through the whole array sorting it again. Since right when the rank array is empty, we hav e been maintaining the order, we can safely assume that if the updated vote is smaller than the next, we can swap position and check the next and so forth.