Exercism - Difference Of Squares(with.Kotlin)

[문제]

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.

 

[Solution1]

import kotlin.math.pow

class Squares(num: Int) {

    private val numList = (1..num)

    fun squareOfSum(): Int = numList.sum().toDouble().pow(2).toInt()

    fun sumOfSquares(): Int = numList.map { it.toDouble().pow(2) }.sum().toInt()

    fun difference(): Int = squareOfSum() - sumOfSquares()

}

처음 시도시에는 toDouble().pow(2)를 사용하여 제곱 처리를 함

 

 

[Solution2]

class Squares(num: Int) {

    private val numList = (1..num)

    fun squareOfSum(): Int = numList.sum().squareWithInt()

    fun sumOfSquares(): Int = numList.sumBy { it.squareWithInt() }

    fun difference(): Int = squareOfSum() - sumOfSquares()

}

private fun Int.squareWithInt(): Int = this * this

 

Extention 을 사용해서 제곱을 처리하고 Map 과 Sum 을 sumBy 를 사용해서 처리하라는 조언에 따라 수정