Add excercise and first solution

Author: programmiri

difference-of-squares/.eslintrc

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+{
+  "root": true,
+  "parser": "babel-eslint",
+  "parserOptions": {
+    "ecmaVersion": 7,
+    "sourceType": "module"
+  },
+  "env": {
+    "es6": true,
+    "node": true,
+    "jest": true
+  },
+  "extends": [
+    "eslint:recommended",
+    "plugin:import/errors",
+    "plugin:import/warnings"
+  ],
+  "rules": {
+    "linebreak-style": "off",
+
+    "import/extensions": "off",
+    "import/no-default-export": "off",
+    "import/no-unresolved": "off",
+    "import/prefer-default-export": "off"
+  }
+}

difference-of-squares/README.md

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+# Difference Of Squares
+
+Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
+
+The square of the sum of the first ten natural numbers is
+(1 + 2 + ... + 10)² = 55² = 3025.
+
+The sum of the squares of the first ten natural numbers is
+1² + 2² + ... + 10² = 385.
+
+Hence the difference between the square of the sum of the first
+ten natural numbers and the sum of the squares of the first ten
+natural numbers is 3025 - 385 = 2640.
+
+You are not expected to discover an efficient solution to this yourself from
+first principles; research is allowed, indeed, encouraged. Finding the best
+algorithm for the problem is a key skill in software engineering.
+
+## Setup
+
+Go through the setup instructions for Javascript to install the necessary
+dependencies:
+
+[https://exercism.io/tracks/javascript/installation](https://exercism.io/tracks/javascript/installation)
+
+## Requirements
+
+Install assignment dependencies:
+
+```bash
+$ npm install
+```
+
+## Making the test suite pass
+
+Execute the tests with:
+
+```bash
+$ npm test
+```
+
+In the test suites all tests but the first have been skipped.
+
+Once you get a test passing, you can enable the next one by changing `xtest` to
+`test`.
+
+## Source
+
+Problem 6 at Project Euler [http://projecteuler.net/problem=6](http://projecteuler.net/problem=6)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have
+completed the exercise.

difference-of-squares/babel.config.js

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+module.exports = {
+  presets: [
+    [
+      '@babel/env',
+      {
+        targets: {
+          node: 'current',
+        },
+        useBuiltIns: false,
+      },
+
+    ],
+  ],
+};

difference-of-squares/difference-of-squares.js

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+export class Squares {
+  constructor(number) {
+    this.number = number;
+  }
+
+  get sumOfSquares() {
+    let count = 0;
+    for (let i = 1; i <= this.number; i++ ) {
+      count += i * i
+    }
+    return count;
+  }
+
+  get squareOfSum() {
+    let count = 0;
+    for (let i = 1; i <= this.number; i++ ) {
+      count += i
+    }
+    return count * count;
+  }
+
+  get difference() {
+    return  this.squareOfSum - this.sumOfSquares
+  }
+}

difference-of-squares/difference-of-squares.spec.js

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+import { Squares } from './difference-of-squares';
+
+describe('difference-of-squares', () => {
+  const squares1 = new Squares(1);
+  const squares5 = new Squares(5);
+  const squares100 = new Squares(100);
+
+  describe('Square the sum of the numbers up to the given number', () => {
+    test('square of sum 1', () => {
+      expect(squares1.squareOfSum).toBe(1);
+    });
+
+    test('square of sum 5', () => {
+      expect(squares5.squareOfSum).toBe(225);
+    });
+
+    test('square of sum 100', () => {
+      expect(squares100.squareOfSum).toBe(25502500);
+    });
+  });
+
+  describe('Sum the squares of the numbers up to the given number', () => {
+    test('sum of squares 1', () => {
+      expect(squares1.sumOfSquares).toBe(1);
+    });
+
+    test('sum of squares 5', () => {
+      expect(squares5.sumOfSquares).toBe(55);
+    });
+
+    test('sum of squares 100', () => {
+      expect(squares100.sumOfSquares).toBe(338350);
+    });
+  });
+
+  describe('Subtract sum of squares from square of sums', () => {
+    test('difference of squares 1', () => {
+      expect(squares1.difference).toBe(0);
+    });
+
+   test('difference of squares 5', () => {
+      expect(squares5.difference).toBe(170);
+    });
+
+   test('difference of squares 100', () => {
+      expect(squares100.difference).toBe(25164150);
+    });
+  });
+});

difference-of-squares/package.json

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+{
+  "name": "exercism-javascript",
+  "description": "Exercism exercises in Javascript.",
+  "author": "Katrina Owen",
+  "private": true,
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/exercism/javascript"
+  },
+  "devDependencies": {
+    "@babel/cli": "^7.5.5",
+    "@babel/core": "^7.5.5",
+    "@babel/preset-env": "^7.5.5",
+    "@types/jest": "^24.0.16",
+    "@types/node": "^12.6.8",
+    "babel-eslint": "^10.0.2",
+    "babel-jest": "^24.8.0",
+    "eslint": "^6.1.0",
+    "eslint-plugin-import": "^2.18.2",
+    "jest": "^24.8.0"
+  },
+  "jest": {
+    "modulePathIgnorePatterns": [
+      "package.json"
+    ]
+  },
+  "scripts": {
+    "test": "jest --no-cache ./*",
+    "watch": "jest --no-cache --watch ./*",
+    "lint": "eslint .",
+    "lint-test": "eslint . && jest --no-cache ./* "
+  },
+  "license": "MIT",
+  "dependencies": {}
+}