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bdf74's solution

to Difference Of Squares in the TypeScript Track

Published at Jul 18 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution 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 TypeScript to install the necessary dependencies:

http://exercism.io/languages/typescript

Requirements

Install assignment dependencies:

$ yarn install

Making the test suite pass

Execute the tests with:

$ yarn test

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.test.ts

import Squares from './difference-of-squares'

describe('Squares', () => {

  describe('up to 5', () => {
    const squares = new Squares(5)

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

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

    xit('gets the difference', () => {
      expect(squares.difference).toBe(170)
    })

  })

  describe('up to 10', () => {
    const squares = new Squares(10)

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

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

    xit('gets the difference', () => {
      expect(squares.difference).toBe(2640)
    })

  })

  describe('up to 100', () => {
    const squares = new Squares(100)

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

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

    xit('gets the difference', () => {
      expect(squares.difference).toBe(25164150)
    })

  })

})
class Squares {

    public myNumber: number
    public myRange: number[]
    public squareOfSums: number
    public sumOfSquares: number
    public difference: number

    constructor(myNumber: number) {
        this.myNumber = myNumber
        this.myRange = [...Array(myNumber).keys()].map( (x) => x + 1 )
        this.squareOfSums = this.calculateSquareOfSums()
        this.sumOfSquares = this.calculateSumOfSquares()
        this.difference = this.squareOfSums - this.sumOfSquares
    }

    calculateSquareOfSums(): number {
        return Math.pow(this.myRange.reduce((a, b) => a + b ), 2)
    }

    calculateSumOfSquares(): number {
        return this.myRange.map( (x) => Math.pow(x, 2)).reduce((a, b) => a + b)
    }

    calculateDifference(): number {
        return 0
    }
}
export default Squares

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