[SCALA-649] Convert a Number to Roman Numeral in Scala (#1455)

* [SCALA-649] Convert a Number to Roman Numeral in Scala

* Renamed test to UnitTest

---------

Co-authored-by: Callum Gibbons <[email protected]>

Author: cawpat

scala-core-modules/scala-core-numbers/src/main/scala/com/baeldung/scala/romannumerals/NumberToRomanNumeral.scala

@@ -0,0 +1,58 @@
+package com.baeldung.scala.romannumerals
+
+import scala.annotation.tailrec
+import scala.math.BigDecimal.int2bigDecimal
+
+object NumberToRomanNumeral {
+
+  private val numbersToRomans = List(
+    (1000, "M"),
+    (900, "CM"),
+    (500, "D"),
+    (400, "CD"),
+    (100, "C"),
+    (90, "XC"),
+    (50, "L"),
+    (40, "XL"),
+    (10, "X"),
+    (9, "IX"),
+    (5, "V"),
+    (4, "IV"),
+    (1, "I")
+  )
+
+  def usingRecursion(num: Int): String = {
+    numbersToRomans.find((n, _) => {
+      num - n >= 0
+    }) match
+      case Some((n, r)) => r + usingRecursion(num - n)
+      case None         => ""
+  }
+
+  def usingTailRecursion(num: Int): String = {
+    @tailrec
+    def recursiveFn(remaining: Int, acc: String): String = {
+      numbersToRomans.find((n, _) => {
+        remaining - n >= 0
+      }) match
+        case Some((n, r)) => recursiveFn(remaining - n, acc + r)
+        case None         => acc
+    }
+    recursiveFn(num, "")
+  }
+
+  def usingFold(num: Int): String = {
+    numbersToRomans
+      .foldLeft((num, ""))((remainingAndAcc, numAndRoman) => {
+        val (remaining, acc) = remainingAndAcc
+        if (remaining == 0) remainingAndAcc
+        else {
+          val (n, r) = numAndRoman
+
+          (remaining % n, acc + r * (remaining / n))
+        }
+      })
+      ._2
+  }
+
+}

scala-core-modules/scala-core-numbers/src/test/scala/com/baeldung/scala/romannumeral/NumberToRomanNumeralUnitTest.scala

@@ -0,0 +1,61 @@
+package com.baeldung.scala.romannumeral
+
+import com.baeldung.scala.romannumerals.NumberToRomanNumeral
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.prop.TableDrivenPropertyChecks
+import org.scalatest.wordspec.AnyWordSpec
+
+class NumberToRomanNumeralUnitTest
+  extends AnyWordSpec
+  with Matchers
+  with TableDrivenPropertyChecks {
+  val testValuesWithResults = Table(
+    ("Number", "Roman"),
+    (0, ""),
+    (1, "I"),
+    (2, "II"),
+    (4, "IV"),
+    (5, "V"),
+    (6, "VI"),
+    (9, "IX"),
+    (10, "X"),
+    (11, "XI"),
+    (14, "XIV"),
+    (15, "XV"),
+    (17, "XVII"),
+    (19, "XIX"),
+    (20, "XX"),
+    (40, "XL"),
+    (44, "XLIV"),
+    (49, "XLIX"),
+    (50, "L"),
+    (90, "XC"),
+    (100, "C"),
+    (400, "CD"),
+    (500, "D"),
+    (900, "CM"),
+    (1000, "M"),
+    (1949, "MCMXLIX")
+  )
+
+  "Correction roman numeral should be returned for number" should {
+    "using usingRecursion" in {
+      forAll(testValuesWithResults)((num, roman) => {
+        NumberToRomanNumeral.usingRecursion(num) shouldBe roman
+      })
+    }
+
+    "using usingTailRecursion" in {
+      forAll(testValuesWithResults)((num, roman) => {
+        NumberToRomanNumeral.usingTailRecursion(num) shouldBe roman
+      })
+    }
+
+    "using usingFold" in {
+      forAll(testValuesWithResults)((num, roman) => {
+        NumberToRomanNumeral.usingFold(num) shouldBe roman
+      })
+    }
+  }
+
+}