Avatar of domnikl

domnikl's solution

to Sum Of Multiples in the Kotlin Track

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

Given a number, find the sum of all the unique multiples of particular numbers up to but not including that number.

If we list all the natural numbers below 20 that are multiples of 3 or 5, we get 3, 5, 6, 9, 10, 12, 15, and 18.

The sum of these multiples is 78.

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

A variation on Problem 1 at Project Euler http://projecteuler.net/problem=1

Submitting Incomplete Solutions

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

SumOfMultiplesTest.kt

import org.junit.Ignore
import org.junit.Test
import kotlin.test.assertEquals

class SumOfMultiplesTest {

    @Test
    fun `multiples of 3 or 5 up to 1`() {
        assertEquals(0, SumOfMultiples.sum(setOf(3, 5), 1))
    }

    @Test
    @Ignore
    fun `multiples of 3 or 5 up to 4`() {
        assertEquals(3, SumOfMultiples.sum(setOf(3, 5), 4))
    }

    @Test
    @Ignore
    fun `multiples of 3 up to 7`() {
        assertEquals(9, SumOfMultiples.sum(setOf(3), 7))
    }

    @Test
    @Ignore
    fun `multiples of 3 or 5 up to 10`() {
        assertEquals(23, SumOfMultiples.sum(setOf(3, 5), 10))
    }

    @Test
    @Ignore
    fun `multiples of 3 or 5 up to 100`() {
        assertEquals(2318, SumOfMultiples.sum(setOf(3, 5), 100))
    }

    @Test
    @Ignore
    fun `multiples of 3 or 5 up to 1000`() {
        assertEquals(233168, SumOfMultiples.sum(setOf(3, 5), 1000))
    }

    @Test
    @Ignore
    fun `multiples of 7, 13 or 17 up to 20`() {
        assertEquals(51, SumOfMultiples.sum(setOf(7, 13, 17), 20))
    }

    @Test
    @Ignore
    fun `multiples of 4 or 6 up to 15`() {
        assertEquals(30, SumOfMultiples.sum(setOf(4, 6), 15))
    }

    @Test
    @Ignore
    fun `multiples of 5, 6 or 8 up to 150`() {
        assertEquals(4419, SumOfMultiples.sum(setOf(5, 6, 8), 150))
    }

    @Test
    @Ignore
    fun `multiples of 5 or 25 up to 51`() {
        assertEquals(275, SumOfMultiples.sum(setOf(5, 25), 51))
    }

    @Test
    @Ignore
    fun `multiples of 43 or 47 up to 10000`() {
        assertEquals(2203160, SumOfMultiples.sum(setOf(43, 47), 10000))
    }

    @Test
    @Ignore
    fun `multiples of 1 up to 100`() {
        assertEquals(4950, SumOfMultiples.sum(setOf(1), 100))
    }

    @Test
    @Ignore
    fun `multiples of an empty set up to 10000`() {
        assertEquals(0, SumOfMultiples.sum(emptySet(), 10000))
    }

}
object SumOfMultiples {
    fun sum(of: Set<Int>, i: Int): Int {
        return of.map { sequence(it).takeWhile { x -> x < i }.toList() }.flatten().toSet().sum()
    }

    private fun sequence(base: Int): Sequence<Int> {
        var i = 0
        return generateSequence { base * ++i }
    }
}

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’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?