refactor: Enhance docs, add tests in MajorityElement

src/main/java/com/thealgorithms/datastructures/hashmap/hashing/MajorityElement.java

@@ -3,19 +3,23 @@
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
-/*
-This class finds the majority element(s) in an array of integers.
-A majority element is an element that appears more than or equal to n/2 times, where n is the length
-of the array.
-*/
+
+/**
+ * This class provides a method to find the majority element(s) in an array of integers.
+ * A majority element is defined as an element that appears at least ⌊n/2⌋ times,
+ * where n is the length of the array. If multiple elements qualify as majority elements,
+ * they are all returned in a list.
+ */
 public final class MajorityElement {
     private MajorityElement() {
     }
-    /*
-   This method returns the majority element(s) in the given array of integers.
-   @param nums: an array of integers
-   @return a list of majority elements
-   */
+
+    /**
+     * Returns a list of majority element(s) from the given array of integers.
+     *
+     * @param nums an array of integers
+     * @return a list containing the majority element(s); returns an empty list if none exist
+     */
     public static List<Integer> majority(int[] nums) {
         HashMap<Integer, Integer> numToCount = new HashMap<>();
         for (final var num : nums) {

src/test/java/com/thealgorithms/datastructures/hashmap/hashing/MajorityElementTest.java

@@ -42,4 +42,39 @@ void testMajorityWithEmptyArray() {
         List<Integer> actual = MajorityElement.majority(nums);
         assertEquals(expected, actual);
     }
+
+    @Test
+    void testMajorityWithAllElementsSame() {
+        int[] nums = {5, 5, 5, 5, 5};
+        List<Integer> expected = new ArrayList<>();
+        expected.add(5);
+        List<Integer> actual = MajorityElement.majority(nums);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void testMajorityWithEvenCountAndOneMajorityElement() {
+        int[] nums = {1, 2, 2, 3, 3, 2};
+        List<Integer> expected = new ArrayList<>();
+        expected.add(2);
+        List<Integer> actual = MajorityElement.majority(nums);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void testMajorityWithNoElementsEqualToHalf() {
+        int[] nums = {1, 1, 2, 2, 3, 3, 4};
+        List<Integer> expected = Collections.emptyList();
+        List<Integer> actual = MajorityElement.majority(nums);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void testMajorityWithLargeArray() {
+        int[] nums = {1, 2, 3, 1, 1, 1, 2, 1, 1};
+        List<Integer> expected = new ArrayList<>();
+        expected.add(1);
+        List<Integer> actual = MajorityElement.majority(nums);
+        assertEquals(expected, actual);
+    }
 }