Adds an integer to roman converter utility

src/main/java/net/knarcraft/knarlib/util/IntegerToRomanUtil.java

@@ -0,0 +1,74 @@
+package net.knarcraft.knarlib.util;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.List;
+
+/**
+ * A utility for converting from an integer to a roman numeral
+ */
+public final class IntegerToRomanUtil {
+
+    private final static List<Integer> romanValues = List.of(1000, 500, 100, 50, 10, 5, 1);
+    private final static List<Character> romanCharacters = List.of('M', 'D', 'C', 'L', 'X', 'V', 'I');
+
+    private IntegerToRomanUtil() {
+
+    }
+
+    /**
+     * Gets the given number as a roman number string
+     *
+     * @param number <p>The number to convert</p>
+     * @return <p>The roman representation of the number</p>
+     */
+    @NotNull
+    public static String getRomanNumber(int number) {
+        StringBuilder output = new StringBuilder();
+        int remainder = number;
+        for (int i = 0; i < romanCharacters.size(); i++) {
+            int romanValue = romanValues.get(i);
+            char romanCharacter = romanCharacters.get(i);
+
+            // Repeat the roman character, and calculate the new remainder
+            if (remainder >= romanValue) {
+                output.append(repeat(romanCharacter, remainder / romanValue));
+                remainder = remainder % romanValue;
+            }
+
+            // Exit early to prevent unexpected trailing characters
+            if (remainder == 0) {
+                return output.toString();
+            }
+
+            // Generate the special case IV and similar
+            for (int j = i; j < romanCharacters.size(); j++) {
+                int value = romanValues.get(j);
+                int difference = Math.max(romanValue - value, 0);
+                
+                /* If the remainder is "one" less than the current roman value, we hit the IV/IX/XL case.
+                   Note that 5 triggers the special case when 10 is tested, as 5 = 10 - 5, which requires a test, so it
+                   can be filtered out. */
+                if (remainder == difference && value != romanValue / 2) {
+                    output.append(romanCharacters.get(j)).append(romanCharacter);
+                    remainder = 0;
+                }
+            }
+        }
+
+        return output.toString();
+    }
+
+    /**
+     * Repeats the given character
+     *
+     * @param character <p>The character to repeat</p>
+     * @param times     <p>The number of times to repeat the character</p>
+     * @return <p>The repeated string</p>
+     */
+    @NotNull
+    private static String repeat(char character, int times) {
+        return String.valueOf(character).repeat(Math.max(0, times));
+    }
+
+}

src/test/java/net/knarcraft/knarlib/util/IntegerToRomanUtilTest.java

@@ -0,0 +1,44 @@
+package net.knarcraft.knarlib.util;
+
+import org.junit.jupiter.api.Test;
+
+import static net.knarcraft.knarlib.util.IntegerToRomanUtil.getRomanNumber;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * A test class for IntegerToRomanConverter
+ */
+public class IntegerToRomanUtilTest {
+
+    @Test
+    public void basicNumbersTest() {
+        assertEquals("I", getRomanNumber(1));
+        assertEquals("II", getRomanNumber(2));
+        assertEquals("III", getRomanNumber(3));
+        assertEquals("IV", getRomanNumber(4));
+        assertEquals("V", getRomanNumber(5));
+        assertEquals("X", getRomanNumber(10));
+        assertEquals("XI", getRomanNumber(11));
+        assertEquals("XII", getRomanNumber(12));
+        assertEquals("XIII", getRomanNumber(13));
+        assertEquals("XIV", getRomanNumber(14));
+        assertEquals("XV", getRomanNumber(15));
+        assertEquals("XX", getRomanNumber(20));
+        assertEquals("L", getRomanNumber(50));
+        assertEquals("C", getRomanNumber(100));
+        assertEquals("D", getRomanNumber(500));
+        assertEquals("M", getRomanNumber(1000));
+    }
+
+    @Test
+    public void nineFourTest() {
+        assertEquals("IV", getRomanNumber(4));
+        assertEquals("IX", getRomanNumber(9));
+        assertEquals("XIV", getRomanNumber(14));
+        assertEquals("XIX", getRomanNumber(19));
+        assertEquals("XXIV", getRomanNumber(24));
+        assertEquals("XL", getRomanNumber(40));
+        assertEquals("IL", getRomanNumber(49));
+    }
+
+}