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to Perfect Numbers in the Kotlin Track

Published at Oct 16 2019 · 0 comments
Instructions
Test suite
Solution

Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for natural numbers.

The Greek mathematician Nicomachus devised a classification scheme for natural numbers, identifying each as belonging uniquely to the categories of perfect, abundant, or deficient based on their aliquot sum. The aliquot sum is defined as the sum of the factors of a number not including the number itself. For example, the aliquot sum of 15 is (1 + 3 + 5) = 9

  • Perfect: aliquot sum = number
    • 6 is a perfect number because (1 + 2 + 3) = 6
    • 28 is a perfect number because (1 + 2 + 4 + 7 + 14) = 28
  • Abundant: aliquot sum > number
    • 12 is an abundant number because (1 + 2 + 3 + 4 + 6) = 16
    • 24 is an abundant number because (1 + 2 + 3 + 4 + 6 + 8 + 12) = 36
  • Deficient: aliquot sum < number
    • 8 is a deficient number because (1 + 2 + 4) = 7
    • Prime numbers are deficient

Implement a way to determine whether a given number is perfect. Depending on your language track, you may also need to implement a way to determine whether a given number is abundant or deficient.

Setup

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

https://exercism.io/tracks/kotlin/installation

Making the test suite pass

Execute the tests with:

$ gradlew test

Use gradlew.bat if you're on Windows

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the @Ignore annotation.

Source

Taken from Chapter 2 of Functional Thinking by Neal Ford. http://shop.oreilly.com/product/0636920029687.do

Submitting Incomplete Solutions

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

NaturalNumberTest.kt

import org.junit.Ignore
import org.junit.Test

import org.junit.Assert.assertEquals

class NaturalNumberTest {

    @Test
    fun smallPerfectNumberIsClassifiedCorrectly() {
        assertEquals(Classification.PERFECT, classify(6))
    }

    @Ignore
    @Test
    fun mediumPerfectNumberIsClassifiedCorrectly() {
        assertEquals(Classification.PERFECT, classify(28))
    }

    @Ignore
    @Test
    fun largePerfectNumberIsClassifiedCorrectly() {
        assertEquals(Classification.PERFECT, classify(33550336))
    }

    @Ignore
    @Test
    fun smallAbundantNumberIsClassifiedCorrectly() {
        assertEquals(Classification.ABUNDANT, classify(12))
    }

    @Ignore
    @Test
    fun mediumAbundantNumberIsClassifiedCorrectly() {
        assertEquals(Classification.ABUNDANT, classify(30))
    }

    @Ignore
    @Test
    fun largeAbundantNumberIsClassifiedCorrectly() {
        assertEquals(Classification.ABUNDANT, classify(33550335))
    }

    @Ignore
    @Test
    fun smallestPrimeDeficientNumberIsClassifiedCorrectly() {
        assertEquals(Classification.DEFICIENT, classify(2))
    }

    @Ignore
    @Test
    fun smallestNonPrimeDeficientNumberIsClassifiedCorrectly() {
        assertEquals(Classification.DEFICIENT, classify(4))
    }

    @Ignore
    @Test
    fun mediumNumberIsClassifiedCorrectly() {
        assertEquals(Classification.DEFICIENT, classify(32))
    }

    @Ignore
    @Test
    fun largeDeficientNumberIsClassifiedCorrectly() {
        assertEquals(Classification.DEFICIENT, classify(33550337))
    }

    @Ignore
    @Test
    fun edgeCaseWithNoFactorsOtherThanItselfIsClassifiedCorrectly() {
        assertEquals(Classification.DEFICIENT, classify(1))
    }

    @Ignore
    @Test(expected = RuntimeException::class)
    fun zeroIsNotANaturalNumber() {
        classify(0)
    }

    @Ignore
    @Test(expected = RuntimeException::class)
    fun negativeNumberIsNotANaturalNumber() {
        classify(-1)
    }

}
enum class Classification {
    DEFICIENT, PERFECT, ABUNDANT
}

fun classify(naturalNumber: Int): Classification {
    require(naturalNumber > 0)
    return (1 until naturalNumber).filter{naturalNumber % it == 0}.sum().let {
        when
        {
           it == naturalNumber -> Classification.PERFECT
           it < naturalNumber -> Classification.DEFICIENT
           else -> Classification.ABUNDANT
        }
    }
}

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