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# rootulp's solution

## to Difference Of Squares in the TypeScript 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)Â² = 55Â² = 3025.

The sum of the squares of the first ten natural numbers is 1Â² + 2Â² + ... + 10Â² = 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 squareOfSums: number
public sumOfSquares: number
public difference: number

constructor(num: number) {
this.squareOfSums = Squares.squareOfSums(num)
this.sumOfSquares = Squares.sumOfSquares(num)
this.difference = this.squareOfSums - this.sumOfSquares
}

private static squareOfSums(num: number): number {
return Squares.square(Squares.sum(Squares.range(num)))
}

private static sumOfSquares(num: number): number {
return Squares.sum(Squares.range(num).map( (x) => Squares.square(x)))
}

private static range(num: number): number[] {
return [...Array(num + 1).keys()]
}

private static sum(num: number[]): number {
return num.reduce((a, b) => a + b, 0)
}

private static square(num: number): number {
return num ** 2
}

}

export default Squares``````

## Community comments

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