BAEL-1815: RomanNumeral and RomanArabicConverter (#4565)

* BAEL-1815: RomanNumeral and RomanArabicConverter

* Refactored getReverseSortedValues

algorithms/src/main/java/com/baeldung/algorithms/romannumerals/RomanArabicConverter.java

@@ -0,0 +1,52 @@
+package com.baeldung.algorithms.romannumerals;
+
+import java.util.List;
+
+class RomanArabicConverter {
+
+    public static int romanToArabic(String input) {
+        String romanNumeral = input.toUpperCase();
+        int result = 0;
+        
+        List<RomanNumeral> romanNumerals = RomanNumeral.getReverseSortedValues();
+
+        int i = 0;
+
+        while ((romanNumeral.length() > 0) && (i < romanNumerals.size())) {
+            RomanNumeral symbol = romanNumerals.get(i);
+            if (romanNumeral.startsWith(symbol.name())) {
+                result += symbol.getValue();
+                romanNumeral = romanNumeral.substring(symbol.name().length());
+            } else {
+                i++;
+            }
+        }
+        if (romanNumeral.length() > 0) {
+            throw new IllegalArgumentException(input + " cannot be converted to a Roman Numeral");
+        }
+
+        return result;
+    }
+
+    public static String arabicToRoman(int number) {
+        if ((number <= 0) || (number > 4000)) {
+            throw new IllegalArgumentException(number + " is not in range (0,4000]");
+        }
+
+        List<RomanNumeral> romanNumerals = RomanNumeral.getReverseSortedValues();
+
+        int i = 0;
+        StringBuilder sb = new StringBuilder();
+
+        while (number > 0 && i < romanNumerals.size()) {
+            RomanNumeral currentSymbol = romanNumerals.get(i);
+            if (currentSymbol.getValue() <= number) {
+                sb.append(currentSymbol.name());
+                number -= currentSymbol.getValue();
+            } else {
+                i++;
+            }
+        }
+        return sb.toString();
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/romannumerals/RomanNumeral.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.romannumerals;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+enum RomanNumeral {
+    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);
+
+    private int value;
+
+    RomanNumeral(int value) {
+        this.value = value;
+    }
+
+    public int getValue() {
+        return value;
+    }
+    
+    public static List<RomanNumeral> getReverseSortedValues() {
+        return Arrays.stream(values())
+          .sorted(Comparator.comparing((RomanNumeral e) -> e.value).reversed())
+          .collect(Collectors.toList());
+    }
+}

algorithms/src/test/java/com/baeldung/algorithms/romannumerals/RomanArabicConverterUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.algorithms.romannumerals;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class RomanArabicConverterUnitTest {
+
+    @Test
+    public void given2018Roman_WhenConvertingToArabic_ThenReturn2018() {
+
+        String roman2018 = "MMXVIII";
+
+        int result = RomanArabicConverter.romanToArabic(roman2018);
+
+        assertThat(result).isEqualTo(2018);
+    }
+
+    @Test
+    public void given1999Arabic_WhenConvertingToRoman_ThenReturnMCMXCIX() {
+
+        int arabic1999 = 1999;
+
+        String result = RomanArabicConverter.arabicToRoman(arabic1999);
+
+        assertThat(result).isEqualTo("MCMXCIX");
+    }
+
+}