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Published at Jul 13 2018
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Instructions

Test suite

Solution

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.

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

http://exercism.io/languages/typescript

Install assignment dependencies:

```
$ yarn install
```

Execute the tests with:

```
$ yarn test
```

Problem 6 at Project Euler http://projecteuler.net/problem=6

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
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
```

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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