Javascript at HackerRank

Javascript at HackerRank

by John Vincent


Posted on May 26, 2018



How to work efficiently with HackerRank Challenges

I have created a pattern to enable quicker challenge resolutions.

HackerRank

HackerRank

Visual Studio Code Notes

HackerRank Github

Chai Notes

Setup

Base: ~/MyDevelopment/github/ui/hackerrank

I use this as the Visual Studio Code workspace.

Create development directories

cd ~/MyDevelopment/github/ui/hackerrank
src/easy
src/medium
src/hard

ESLint Configuration

cd ~/MyDevelopment/github/ui/hackerrank

Create .eslintrc.json

{
	"extends": [
		"airbnb",
		"prettier"
	],
	"env": {
		"node": true,
		"browser": false,
		"es6": true
	},
	"globals": {},
	"rules": {
		"no-console": 0,
		"max-len": [
			"error",
			{
				"code": 120,
				"tabWidth": 2,
				"comments": 120
			}
		],
		"indent": [
			2,
			"tab",
			{
				"SwitchCase": 1
			}
		],
		"no-tabs": 0
	},
	"plugins": []
}

Development

cd ~/MyDevelopment/github/ui/hackerrank
mkdir src
cd src

npm init

npm i chai --save-dev
npm i chai-http --save-dev
npm i faker --save-dev
npm i mocha --save-dev
npm i jsdoc --save-dev

Create challenge

I have put all my HackerRank challenges into

⁨MyDevelopment/⁨github/⁨ui/⁨hackerrank⁩/src/{challenge-difficulty}/{challenge-name}

challenge-difficulty is type easy, medium, hard

Basic Template


/*
{Challenge URL}

{Challenge name}
*/

/* eslint-disable no-plusplus */

const convert = {};

let inputString = '';
let currentLine = 0;

function readLine() {
	console.error('inputString[currentLine] ', inputString[currentLine]);
	return inputString[currentLine++];
}

function minimumDistances(a) {}	// replace from challenge

convert.main = function main(input) {
	currentLine = 0;
	inputString = input;

/* insert from challenge */

	console.log(`result ${result}\n`);
	return result;
}

module.exports = convert;

or

function main(input) {
	currentLine = 0;
	inputString = input;

/* insert from challenge */

	console.log(`result ${result}\n`);
	return result;
}

module.exports = {
	main,
	anotherFunction
};

Code

Copy the template to a.js and begin work.

Run the app to verify it runs:

node a

Console Messages

To see console messages, use console.error

For example:

console.error('t1 ', t1, ' t2 ', t2);

Unit Test Code

The above technique allows for the creation of unit tests.

Each challenge has sample input and outputs.

Use const input for the sample input

Verify the result using chai

Always add unit tests to cover every condition described.

Basic Template for Unit Tests

Copy to test/test.js


/* global describe, it */

const should = require('chai').should();

const a = require('../a');

describe('test', () => {
	it('1', () => {
		const input = [
			'8',
			'1 2 3 4 3 3 2 1'
		];
		const result = a.main(input);
		result.should.be.a('array');
		result.length.should.equal(4);
		result[0].should.equal(8);
		result[1].should.equal(6);
		result[2].should.equal(4);
		result[3].should.equal(1);
	});

	it('2', () => {
		const input = [
			'6',
			'5 4 4 2 2 8'
		];
		const result = a.main(input);
		result.should.be.a('array');
		result.length.should.equal(4);
		result[0].should.equal(6);
		result[1].should.equal(4);
		result[2].should.equal(2);
		result[3].should.equal(1);
	});
});

describe('test', () => {
	it('1', () => {
		const input = [
			'6',
			'7 1 3 4 1 7'
		];
		const result = a.main(input);
		result.should.equal(3);
	});
});

Run the Unit Tests

Create script mocha to run the unit tests

../../node_modules/mocha/bin/mocha test

To run the tests

./mocha

Use Debugger

  • Debug icon (left nav)
  • Gear icon (top of debug view)
  • Which edits launch.json

Add the following configuration

{
  "name": "name-of-challenge",
  "type": "node",
  "request": "launch",
  "program": "${workspaceRoot}/src/node_modules/mocha/bin/_mocha",
  "stopOnEntry": false,
  "args": ["src/{difficulty}/name-of-challenge/test/**/*.js", "--no-timeouts"],
  "cwd": "${workspaceRoot}",
  "runtimeExecutable": null,
  "env": { "NODE_ENV": "testing" }
},
  • Debug view (top nav)
  • Set a breakpoint.
  • Select Run name-of-challenge
  • Click on the green arrow icon to start debugging.

Unlock a Testcase

This is necessary sometimes as I cannot possibly think of, or code the vast array of use cases.

cd test
mkdir testcase-{test case number}
  • Unlock a test case
  • Select Download, which opens the data in a new browser tab
  • Copy data to `test/testcase-{test case number}/input.txt

Create test/test-case-{test case number}.js

Basic Template


/* global describe, it, before */

/*
{URL of data download}

test case {test case number}
*/

/* eslint-disable no-plusplus */

const fs = require('fs');
const should = require('chai').should();

const a = require('../a');

const ide = false;	// true if using Visual Studio Code debugger
const inputFilename = ide ? 
	'./src/{challenge-difficulty}/{challenge-name}/test/testcase-{test case number}/input.txt' :
	'./test/testcase-{test case number}/input.txt';

const outputFilename = ide ? 
	'./src/{challenge-difficulty}/{challenge-name}/test/testcase-{test case number}/input.txt' :
	'./test/testcase-{test case number}/output.txt';

let inputString = null;
let outputString = null;

describe('testcase-{test case number}', () => {
	before(() => {
		const alpha = fs.readFileSync(inputFilename).toString();
		inputString = alpha
			.trim()
			.split('\n')
			.map(str => str.trim());
	});

	it('1', () => {
		const result = a.main(inputString);
		result.should.equal(110198);
	});
});

describe('testcase-{test case number}', () => {
	before(() => {
		const alpha = fs.readFileSync(inputFilename).toString();
		inputString = alpha
			.trim()
			.split('\n')
			.map(str => str.trim());

		const beta = fs.readFileSync(outputFilename).toString();
		outputString = beta
			.trim()
			.split('\n')
			.map(str => str.trim());
	});

	it('1', () => {
		const result = a.main(inputString);
		result.should.be.a('array');
		result.length.should.equal(outputString.length);
		for (let cnt = 0; cnt < outputString.length; cnt++) {
			result[cnt].should.equal(outputString[cnt]);
		}
	});
});