refactor: Enhance docs, remove main, add more tests in `IntegerToRo…

src/main/java/com/thealgorithms/conversions/IntegerToRoman.java

@@ -1,68 +1,68 @@
 package com.thealgorithms.conversions;
 
 /**
- * Converting Integers into Roman Numerals
+ * A utility class to convert integers into Roman numerals.
  *
- * <p>
- * ('I', 1); ('IV',4); ('V', 5); ('IX',9); ('X', 10); ('XL',40); ('L', 50);
- * ('XC',90); ('C', 100); ('D', 500); ('M', 1000);
+ * <p>Roman numerals follow these rules:
+ * <ul>
+ *   <li>I = 1</li>
+ *   <li>IV = 4</li>
+ *   <li>V = 5</li>
+ *   <li>IX = 9</li>
+ *   <li>X = 10</li>
+ *   <li>XL = 40</li>
+ *   <li>L = 50</li>
+ *   <li>XC = 90</li>
+ *   <li>C = 100</li>
+ *   <li>D = 500</li>
+ *   <li>M = 1000</li>
+ * </ul>
+ *
+ * <p>Conversion is based on repeatedly subtracting the largest possible Roman numeral value
+ * from the input number until it reaches zero. For example, 1994 is converted as:
+ * <pre>
+ *   1994 -> MCMXCIV (1000 + 900 + 90 + 4)
+ * </pre>
  */
 public final class IntegerToRoman {
+
+    // Array of Roman numeral values in descending order
+    private static final int[] ALL_ROMAN_NUMBERS_IN_ARABIC = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
+
+    // Corresponding Roman numeral symbols
+    private static final String[] ALL_ROMAN_NUMBERS = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
+
     private IntegerToRoman() {
     }
 
-    private static final int[] ALL_ROMAN_NUMBERS_IN_ARABIC = new int[] {
-        1000,
-        900,
-        500,
-        400,
-        100,
-        90,
-        50,
-        40,
-        10,
-        9,
-        5,
-        4,
-        1,
-    };
-    private static final String[] ALL_ROMAN_NUMBERS = new String[] {
-        "M",
-        "CM",
-        "D",
-        "CD",
-        "C",
-        "XC",
-        "L",
-        "XL",
-        "X",
-        "IX",
-        "V",
-        "IV",
-        "I",
-    };
-
-    // Value must be > 0
+    /**
+     * Converts an integer to its Roman numeral representation.
+     * Steps:
+     * <ol>
+     *     <li>Iterate over the Roman numeral values in descending order</li>
+     *     <li>Calculate how many times a numeral fits</li>
+     *     <li>Append the corresponding symbol</li>
+     *     <li>Subtract the value from the number</li>
+     *     <li>Repeat until the number is zero</li>
+     *     <li>Return the Roman numeral representation</li>
+     * </ol>
+     *
+     * @param num the integer value to convert (must be greater than 0)
+     * @return the Roman numeral representation of the input integer
+     *         or an empty string if the input is non-positive
+     */
     public static String integerToRoman(int num) {
         if (num <= 0) {
             return "";
         }
 
         StringBuilder builder = new StringBuilder();
-
-        for (int a = 0; a < ALL_ROMAN_NUMBERS_IN_ARABIC.length; a++) {
-            int times = num / ALL_ROMAN_NUMBERS_IN_ARABIC[a];
-            for (int b = 0; b < times; b++) {
-                builder.append(ALL_ROMAN_NUMBERS[a]);
-            }
-
-            num -= times * ALL_ROMAN_NUMBERS_IN_ARABIC[a];
+        for (int i = 0; i < ALL_ROMAN_NUMBERS_IN_ARABIC.length; i++) {
+            int times = num / ALL_ROMAN_NUMBERS_IN_ARABIC[i];
+            builder.append(ALL_ROMAN_NUMBERS[i].repeat(Math.max(0, times)));
+            num -= times * ALL_ROMAN_NUMBERS_IN_ARABIC[i];
         }
 
         return builder.toString();
     }
-
-    public static void main(String[] args) {
-        System.out.println(IntegerToRoman.integerToRoman(2131));
-    }
 }

src/test/java/com/thealgorithms/conversions/IntegerToRomanTest.java

@@ -10,5 +10,30 @@ public class IntegerToRomanTest {
     public void testIntegerToRoman() {
         assertEquals("MCMXCIV", IntegerToRoman.integerToRoman(1994));
         assertEquals("LVIII", IntegerToRoman.integerToRoman(58));
+        assertEquals("IV", IntegerToRoman.integerToRoman(4));
+        assertEquals("IX", IntegerToRoman.integerToRoman(9));
+        assertEquals("MMM", IntegerToRoman.integerToRoman(3000));
+    }
+
+    @Test
+    public void testSmallNumbers() {
+        assertEquals("I", IntegerToRoman.integerToRoman(1));
+        assertEquals("II", IntegerToRoman.integerToRoman(2));
+        assertEquals("III", IntegerToRoman.integerToRoman(3));
+    }
+
+    @Test
+    public void testRoundNumbers() {
+        assertEquals("X", IntegerToRoman.integerToRoman(10));
+        assertEquals("L", IntegerToRoman.integerToRoman(50));
+        assertEquals("C", IntegerToRoman.integerToRoman(100));
+        assertEquals("D", IntegerToRoman.integerToRoman(500));
+        assertEquals("M", IntegerToRoman.integerToRoman(1000));
+    }
+
+    @Test
+    public void testEdgeCases() {
+        assertEquals("", IntegerToRoman.integerToRoman(0)); // Non-positive number case
+        assertEquals("", IntegerToRoman.integerToRoman(-5)); // Negative number case
     }
 }