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brunnock's solution

to Difference Of Squares in the JavaScript Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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.

Setup

Go through the setup instructions for JavaScript to install the necessary dependencies:

http://exercism.io/languages/javascript/installation

Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

npm install -g jasmine

Run the test suite from the exercise directory with:

jasmine difference-of-squares.spec.js

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing xit to it.

Source

Problem 6 at Project Euler 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.spec.js

var Squares = require('./difference-of-squares');

describe('Squares', function () {
  describe('up to 5', function () {
    var squares = new Squares(5);

    it('gets the square of sums', function () {
      expect(squares.squareOfSums).toBe(225);
    });

    xit('gets the sum of squares', function () {
      expect(squares.sumOfSquares).toBe(55);
    });

    xit('gets the difference', function () {
      expect(squares.difference).toBe(170);
    });
  });

  describe('up to 10', function () {
    var squares = new Squares(10);

    xit('gets the square of sums', function () {
      expect(squares.squareOfSums).toBe(3025);
    });

    xit('gets the sum of squares', function () {
      expect(squares.sumOfSquares).toBe(385);
    });

    xit('gets the difference', function () {
      expect(squares.difference).toBe(2640);
    });
  });

  describe('up to 100', function () {
    var squares = new Squares(100);

    xit('gets the square of sums', function () {
      expect(squares.squareOfSums).toBe(25502500);
    });

    xit('gets the sum of squares', function () {
      expect(squares.sumOfSquares).toBe(338350);
    });

    xit('gets the difference', function () {
      expect(squares.difference).toBe(25164150);
    });
  });
});
function Squares(num){
    this.squareOfSums=0;
    this.sumOfSquares=0;

    for (var x=1; x<=num; ++x) {
	this.squareOfSums += x;
	this.sumOfSquares += x*x;
    }

    this.squareOfSums *= this.squareOfSums;
    this.difference = Math.abs(this.squareOfSums - this.sumOfSquares);
}

module.exports=Squares;

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