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billwanjohi's solution

to Sum Of Multiples in the Scala Track

Published at Jan 04 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.

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command sbt test in the exercise directory.

For more detailed info about the Scala track see the help page.

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.scala

import org.scalatest.{Matchers, FunSuite}

/** @version 1.2.0 */
class SumOfMultiplesTest extends FunSuite with Matchers {

  test("multiples of 3 or 5 up to 1") {
    SumOfMultiples.sum(Set(3, 5), 1) should be(0)
  }

  test("multiples of 3 or 5 up to 4") {
    pending
    SumOfMultiples.sum(Set(3, 5), 4) should be(3)
  }

  test("multiples of 3 up to 7") {
    pending
    SumOfMultiples.sum(Set(3), 7) should be(9)
  }

  test("multiples of 3 or 5 up to 10") {
    pending
    SumOfMultiples.sum(Set(3, 5), 10) should be(23)
  }

  test("multiples of 3 or 5 up to 100") {
    pending
    SumOfMultiples.sum(Set(3, 5), 100) should be(2318)
  }

  test("multiples of 3 or 5 up to 1000") {
    pending
    SumOfMultiples.sum(Set(3, 5), 1000) should be(233168)
  }

  test("multiples of 7, 13 or 17 up to 20") {
    pending
    SumOfMultiples.sum(Set(7, 13, 17), 20) should be(51)
  }

  test("multiples of 4 or 6 up to 15") {
    pending
    SumOfMultiples.sum(Set(4, 6), 15) should be(30)
  }

  test("multiples of 5, 6 or 8 up to 150") {
    pending
    SumOfMultiples.sum(Set(5, 6, 8), 150) should be(4419)
  }

  test("multiples of 5 or 25 up to 51") {
    pending
    SumOfMultiples.sum(Set(5, 25), 51) should be(275)
  }

  test("multiples of 43 or 47 up to 10000") {
    pending
    SumOfMultiples.sum(Set(43, 47), 10000) should be(2203160)
  }

  test("multiples of 1 up to 100") {
    pending
    SumOfMultiples.sum(Set(1), 100) should be(4950)
  }

  test("multiples of an empty list up to 10000") {
    pending
    SumOfMultiples.sum(Set(), 10000) should be(0)
  }
}
object SumOfMultiples {
  def sum(factors: Set[Int], limit: Int): Int = {
    // collect all multiples in combined set
    val multiples = factors.foldLeft(Set(0)) { (acc, x) =>
      acc ++ (0 until limit by x toSet)
    }
    return multiples.sum
  }
}

Community comments

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billwanjohi's Reflection

Not terribly efficient, but gets the job done.