refactor: Enhance docs, add more tests in NumberAppearingOddTimes

src/main/java/com/thealgorithms/bitmanipulation/NumberAppearingOddTimes.java

@@ -1,21 +1,41 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * Find the Number Appearing Odd Times in an array
+ * This class provides a method to find the element that appears an
+ * odd number of times in an array. All other elements in the array
+ * must appear an even number of times for the logic to work.
+ *
+ * The solution uses the XOR operation, which has the following properties:
+ * - a ^ a = 0 (XOR-ing the same numbers cancels them out)
+ * - a ^ 0 = a
+ * - XOR is commutative and associative.
+ *
+ * Time Complexity: O(n), where n is the size of the array.
+ * Space Complexity: O(1), as no extra space is used.
+ *
+ * Usage Example:
+ * int result = NumberAppearingOddTimes.findOddOccurrence(new int[]{1, 2, 1, 2, 3});
+ * // result will be 3
+ *
  * @author Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
  */
 
 public final class NumberAppearingOddTimes {
     private NumberAppearingOddTimes() {
     }
+
+    /**
+     * Finds the element in the array that appears an odd number of times.
+     *
+     * @param arr the input array containing integers, where all elements
+     *            except one appear an even number of times.
+     * @return the integer that appears an odd number of times.
+     */
     public static int findOddOccurrence(int[] arr) {
         int result = 0;
-
-        // XOR all elements in the array
         for (int num : arr) {
             result ^= num;
         }
-
         return result;
     }
 }

src/test/java/com/thealgorithms/bitmanipulation/NumberAppearingOddTimesTest.java

@@ -2,22 +2,48 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 class NumberAppearingOddTimesTest {
 
-    @Test
-    void testFindOddOccurrence() {
-        int[] arr1 = {5, 6, 7, 8};
-        assertEquals(12, NumberAppearingOddTimes.findOddOccurrence(arr1));
+    /**
+     * Parameterized test for findOddOccurrence method. Tests multiple
+     * input arrays and their expected results.
+     */
+    @ParameterizedTest
+    @MethodSource("provideTestCases")
+    void testFindOddOccurrence(int[] input, int expected) {
+        assertEquals(expected, NumberAppearingOddTimes.findOddOccurrence(input));
+    }
+
+    /**
+     * Provides test cases for the parameterized test.
+     * Each test case consists of an input array and the expected result.
+     */
+    private static Stream<Arguments> provideTestCases() {
+        return Stream.of(
+            // Single element appearing odd times (basic case)
+            Arguments.of(new int[] {5, 6, 7, 8, 6, 7, 5}, 8),
+
+            // More complex case with multiple pairs
+            Arguments.of(new int[] {2, 3, 5, 4, 5, 2, 4, 3, 5, 2, 4, 4, 2}, 5),
+
+            // Case with only one element appearing once
+            Arguments.of(new int[] {10, 10, 20, 20, 30}, 30),
+
+            // Negative numbers with an odd occurrence
+            Arguments.of(new int[] {-5, -5, -3, -3, -7, -7, -7}, -7),
 
-        int[] arr2 = {2, 3, 5, 4, 5, 2, 4, 3, 5, 2, 4, 4, 2};
-        assertEquals(5, NumberAppearingOddTimes.findOddOccurrence(arr2));
+            // All elements cancel out to 0 (even occurrences of all elements)
+            Arguments.of(new int[] {1, 2, 1, 2}, 0),
 
-        int[] arr3 = {10, 10, 20, 20, 30};
-        assertEquals(30, NumberAppearingOddTimes.findOddOccurrence(arr3));
+            // Array with a single element (trivial case)
+            Arguments.of(new int[] {42}, 42),
 
-        int[] arr4 = {-5, -5, -3, -3, -7, -7, -7};
-        assertEquals(-7, NumberAppearingOddTimes.findOddOccurrence(arr4));
+            // Large array with repeated patterns
+            Arguments.of(new int[] {1, 1, 2, 2, 3, 3, 3, 4, 4}, 3));
     }
 }