roman numerals kata

RomanNumbersTest.scala

import org.scalatest._

class RomanNumbersTest extends FlatSpec with ShouldMatchers with BeforeAndAfterEach {
  private var numbers: RomanNumbers = _

  override def beforeEach() {
    numbers = new RomanNumbers
  }

  "Roman numbers" should "convert I to 1" in {
    numbers.convert("I") should equal (1)
  }

  it should "convert II" in {
    numbers.convert("II") should equal (2)
  }

  it should "convert III" in {
    numbers.convert("III") should equal (3)
  }

  it should "convert IV" in {
    numbers.convert("IV") should equal (4)
  }

  it should "convert V" in {
    numbers.convert("V") should equal (5)
  }

  it should "convert X" in {
    numbers.convert("X") should equal (10)
  }

  it should "convert IX" in {
    numbers.convert("IX") should equal (9)
  }

  it should "convert VI" in {
    numbers.convert("VI") should equal (6)
  }

  it should "convert VII" in {
    numbers.convert("VII") should equal (7)
  }

  it should "convert VIII" in {
    numbers.convert("VIII") should equal (8)
  }

  it should "convert XI" in {
    numbers.convert("XI") should equal (11)
  }

  it should "convert XX" in {
    numbers.convert("XX") should equal (20)
  }

  it should "convert XXX" in {
    numbers.convert("XXX") should equal (30)
  }

  it should "convert L" in {
    numbers.convert("L") should equal (50)
  }

  it should "convert LX" in {
    numbers.convert("LX") should equal (60)
  }

  it should "convert XL" in {
    numbers.convert("XL") should equal (40)
  }

  it should "convert C" in {
    numbers.convert("C") should equal (100)
  }

  it should "convert CC" in {
    numbers.convert("CC") should equal (200)
  }

  it should "convert XC" in {
    numbers.convert("XC") should equal (90)
  }

  it should "convert CX" in {
    numbers.convert("CX") should equal (110)
  }

  it should "convert D" in {
    numbers.convert("D") should equal (500)
  }

  it should "convert CD" in {
    numbers.convert("CD") should equal (400)
  }

  it should "convert DC" in {
    numbers.convert("DC") should equal (600)
  }

  it should "convert M" in {
    numbers.convert("M") should equal (1000)
  }

  it should "convert CM" in {
    numbers.convert("CM") should equal (900)
  }

  it should "convert MC" in {
    numbers.convert("MC") should equal (1100)
  }

  it should "convert MD" in {
    numbers.convert("MD") should equal (1500)
  }

  it should "convert MM" in {
    numbers.convert("MM") should equal (2000)
  }

  it should "convert MIX" in {
    numbers.convert("MIX") should equal (1009)
  }

  it should "convert MCIX" in {
    numbers.convert("MCIX") should equal (1109)
  }

  it should "convert MCMLXXXIV" in {
    numbers.convert("MCMLXXXIV") should equal (1984)
  }

  it should "convert MMMMMCCCLXVII" in {
    numbers.convert("MMMMMCCCLXVII") should equal (5367)
  }
}

class RomanNumbers {
  def summarize(digits: List[Int]): Int = digits match {
    case x :: Nil => x
    case x :: y :: tail if x >= y => x + summarize(y :: tail)
    case x :: y :: tail if x < y => summarize(y :: tail) - x
  }

  def convert(s: String) = summarize(s.toList.map(convertDigit))

  private def convertDigit(x: Char): Int = x match {
    case 'I' => 1
    case 'V' => 5
    case 'X' => 10
    case 'L' => 50
    case 'C' => 100
    case 'D' => 500
    case 'M' => 1000
  }
}