Arabic-2-Roman

main.swift

extension Int {
  enum RomanDigits: Int, CaseIterable {
    case I = 1
    case IV = 4
    case V = 5
    case IX = 9
    case X = 10
    case XL = 40
    case L = 50
    case XC = 90
    case C = 100
    case CD = 400
    case D = 500
    case CM = 900
    case M = 1000

    static let max: Int = 3999
    static let min: Int = 1
    static let range = min...max
  }

  func romanNumber() -> String {
    guard RomanDigits.range.contains(self) else {
      return "OUT OF RANGE"
    }
    return RomanDigits
      .allCases
      .reversed()
      .reduce(into: (res: "", cnt: self)) { result, digit in
      while result.cnt >= digit.rawValue {
        result.cnt -= digit.rawValue
        result.res += String(describing: digit)
      }
    }.res
  }
}

@discardableResult
func test(_ s1: String, _ s2: Int) -> Bool {
  let condition = s1 == s2.romanNumber()
  print("\(s1) is ROMAN \(s2) : " + (condition ? "PASS" : "FAIL"))
  return condition
}

test("X", 10)
test("VII", 7)
test("MMMCMXCIX", 3999)
test("I", 1)
test("OUT OF RANGE", 0)
test("OUT OF RANGE", 4000)