Scala Coding Dojo files

RomanConvert.scala

object RomanConvert {
  val arabic = List(
    "I" -> 1,
    "IV" -> 4,
    "V" -> 5,
    "IX" -> 9,
    "X" -> 10,
    "XL" -> 40,
    "L" -> 50,
    "XC" -> 90,
    "C" -> 100,
    "CD" -> 400,
    "D" -> 500,
    "CM" -> 900,
    "M" -> 1000
  )
  val roman = arabic.map {
    _.swap
  }
  // Values
  // 1 -> I
  // 5 -> V
  // 10 -> X
  // 50 -> L
  // 100 -> C
  // 500 -> D
  // 1000 -> M

  def toArabic(roman: String): Int = {
    def reduce(acc:Int, number:String, numerals:List[(String, Int)]):Int = {
      if(number.isEmpty) {
        acc
      } else {
        if(number.startsWith(numerals.head._1)){
          reduce( acc+ numerals.head._2, number.replaceFirst(numerals.head._1, ""), numerals)
        } else {
          reduce(acc, number, numerals.tail)
        }
      }
    }
    reduce(0, roman, arabic.reverse)
  }

  def toRoman(number: Int): String = {
    def reduce(acc:String, number:Int, numerals:List[(String, Int)]):String = {
      if(number == 0 || numerals.isEmpty) {
        acc
      } else {
        val count = number/ numerals.head._2
        if(count > 0) {
          reduce(acc + (numerals.head._1 * count), number - numerals.head._2 * count, numerals.tail)
        } else {
          reduce(acc, number, numerals.tail)
        }
      }
    }

    reduce("", number, arabic.reverse)
  }
}

RomanTest.scala

import org.scalatest.{Matchers, FunSpec}

class RomanTest extends FunSpec with Matchers {

  val testCases = Map(
    "III" -> 3,
    "II" -> 2,
    "VIII" -> 8,
    "XXXI" -> 31,
    "XXIX" -> 29,
    "XXXVIII" -> 38,
    "CCXCI" -> 291,
    "MCMXCIX" -> 1999
  )

  describe("Converting arabic numerals to roman numerals") {
    describe("Defining the range of our problem") {
      it("converts the smallest: 1") {
        RomanConvert.toRoman(1) should equal("I")
      }
      it("converts the largest: 3999") {
        RomanConvert.toRoman(3999) should equal("MMMCMXCIX")
      }
    }
    it("converts 2 to II") {
      RomanConvert.toRoman(2) should equal("II")
    }
    it("converts 4 to IV") {
      RomanConvert.toRoman(4) should equal("IV")
    }
    describe("Defining a few test cases") {
      testCases.map(_.swap).foreach { case (arabic: Int, roman: String) =>
        it(s"converts $arabic to $roman") {
          RomanConvert.toRoman(arabic) should equal(roman)
        }
      }
    }
  }

  describe("Converting roman numerals to arabic numerals") {
    describe("Defining the range of our problem") {
      it("converts the smallest: I") {
        RomanConvert.toArabic("I") should equal(1)
      }
      it("converts the largest: MMMCMXCIX") {
        RomanConvert.toArabic("MMMCMXCIX") should equal(3999)
      }
    }
    describe("Converting single roman numerals to arabic") {
      List(("I", 1), ("V", 5), ("X", 10), ("L", 50), ("C", 100), ("D", 500), ("M", 1000)).foreach { case (roman, arabic) =>
        it(s"converts $roman to $arabic") {
          RomanConvert.toArabic(roman) should equal(arabic)
        }
      }
    }
    describe("defining a few test cases") {
      testCases.foreach { case (roman: String, arabic: Int) =>
        it(s"converts $roman to $arabic") {
          RomanConvert.toArabic(roman) should equal(arabic)
        }
      }
    }
  }
}