Enhance docs, add tests in RotateSinglyLinkedLists (#6011)

src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java

@@ -6,67 +6,100 @@ import static org.junit.jupiter.api.Assertions.assertNull;
 import org.junit.jupiter.api.Test;
 
 /**
- * Test cases for RotateSinglyLinkedLists
+ * Test cases for RotateSinglyLinkedLists.
  * Author: Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
  */
 public class RotateSinglyLinkedListsTest {
 
+    private final RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
+
+    // Helper method to create a linked list from an array of values
+    private Node createLinkedList(int[] values) {
+        if (values.length == 0) {
+            return null;
+        }
+
+        Node head = new Node(values[0]);
+        Node current = head;
+        for (int i = 1; i < values.length; i++) {
+            current.next = new Node(values[i]);
+            current = current.next;
+        }
+        return head;
+    }
+
+    // Helper method to convert a linked list to a string for easy comparison
+    private String linkedListToString(Node head) {
+        StringBuilder sb = new StringBuilder();
+        Node current = head;
+        while (current != null) {
+            sb.append(current.value);
+            if (current.next != null) {
+                sb.append(" -> ");
+            }
+            current = current.next;
+        }
+        return sb.toString();
+    }
+
     @Test
     public void testRotateRightEmptyList() {
-        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
-
-        // Test case: Rotate an empty list
+        // Rotate an empty list
         assertNull(rotator.rotateRight(null, 2));
     }
 
     @Test
     public void testRotateRightSingleNodeList() {
-        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
-
-        // Test case: Rotate a list with one element
+        // Rotate a list with a single element
         Node singleNode = new Node(5);
         Node rotatedSingleNode = rotator.rotateRight(singleNode, 3);
-        assertEquals(5, rotatedSingleNode.value);
-        assertNull(rotatedSingleNode.next);
+        assertEquals("5", linkedListToString(rotatedSingleNode));
     }
 
     @Test
     public void testRotateRightMultipleElementsList() {
-        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
-
-        // Test case: Rotate a list with multiple elements (Rotate by 2)
-        Node head = new Node(1);
-        head.next = new Node(2);
-        head.next.next = new Node(3);
-        head.next.next.next = new Node(4);
-        head.next.next.next.next = new Node(5);
-
-        Node rotated1 = rotator.rotateRight(head, 2);
-        assertEquals(4, rotated1.value);
-        assertEquals(5, rotated1.next.value);
-        assertEquals(1, rotated1.next.next.value);
-        assertEquals(2, rotated1.next.next.next.value);
-        assertEquals(3, rotated1.next.next.next.next.value);
-        assertNull(rotated1.next.next.next.next.next);
+        // Rotate a list with multiple elements (rotate by 2)
+        Node head = createLinkedList(new int[] {1, 2, 3, 4, 5});
+        Node rotated = rotator.rotateRight(head, 2);
+        assertEquals("4 -> 5 -> 1 -> 2 -> 3", linkedListToString(rotated));
     }
 
     @Test
     public void testRotateRightFullRotation() {
-        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
+        // Rotate by more than the length of the list
+        Node head = createLinkedList(new int[] {1, 2, 3, 4, 5});
+        Node rotated = rotator.rotateRight(head, 7);
+        assertEquals("4 -> 5 -> 1 -> 2 -> 3", linkedListToString(rotated));
+    }
 
-        // Test case: Rotate a list with multiple elements (Full rotation)
-        Node head = new Node(1);
-        head.next = new Node(2);
-        head.next.next = new Node(3);
-        head.next.next.next = new Node(4);
-        head.next.next.next.next = new Node(5);
+    @Test
+    public void testRotateRightZeroRotation() {
+        // Rotate a list by k = 0 (no rotation)
+        Node head = createLinkedList(new int[] {1, 2, 3, 4, 5});
+        Node rotated = rotator.rotateRight(head, 0);
+        assertEquals("1 -> 2 -> 3 -> 4 -> 5", linkedListToString(rotated));
+    }
 
-        Node rotated3 = rotator.rotateRight(head, 7);
-        assertEquals(4, rotated3.value);
-        assertEquals(5, rotated3.next.value);
-        assertEquals(1, rotated3.next.next.value);
-        assertEquals(2, rotated3.next.next.next.value);
-        assertEquals(3, rotated3.next.next.next.next.value);
-        assertNull(rotated3.next.next.next.next.next);
+    @Test
+    public void testRotateRightByListLength() {
+        // Rotate a list by k equal to list length (no change)
+        Node head = createLinkedList(new int[] {1, 2, 3, 4, 5});
+        Node rotated = rotator.rotateRight(head, 5);
+        assertEquals("1 -> 2 -> 3 -> 4 -> 5", linkedListToString(rotated));
+    }
+
+    @Test
+    public void testRotateRightByMultipleOfListLength() {
+        Node head = createLinkedList(new int[] {1, 2, 3, 4, 5});
+        Node rotated = rotator.rotateRight(head, 10); // k = 2 * list length
+        assertEquals("1 -> 2 -> 3 -> 4 -> 5", linkedListToString(rotated));
+    }
+
+    @Test
+    public void testRotateRightLongerList() {
+        // Rotate a longer list by a smaller k
+        Node head = createLinkedList(new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9});
+        Node rotated = rotator.rotateRight(head, 4);
+        assertEquals("6 -> 7 -> 8 -> 9 -> 1 -> 2 -> 3 -> 4 -> 5", linkedListToString(rotated));
     }
 }