Merge branch 'master' into merge_k_ll_improve

Author: siriak

src/main/java/com/thealgorithms/datastructures/lists/CreateAndDetectLoop.java

@@ -1,11 +1,24 @@
 package com.thealgorithms.datastructures.lists;
 
+/**
+ * CreateAndDetectLoop provides utility methods for creating and detecting loops
+ * (cycles) in a singly linked list. Loops in a linked list are created by
+ * connecting the "next" pointer of one node to a previous node in the list,
+ * forming a cycle.
+ */
 public final class CreateAndDetectLoop {
 
-    // Node class representing a single node in the linked list
+    /**
+     * Private constructor to prevent instantiation of this utility class.
+     */
     private CreateAndDetectLoop() {
         throw new UnsupportedOperationException("Utility class");
     }
+
+    /**
+     * Node represents an individual element in the linked list, containing
+     * data and a reference to the next node.
+     */
     static final class Node {
         int data;
         Node next;
@@ -16,19 +29,16 @@ static final class Node {
         }
     }
 
-    // Method to create a loop between two specific positions in the linked list
-    /*
-     *  Test case that shows the Cycle(loop) in a LinkedList
-     *  Let's take this linked list:
-     *  1->2->3->4->5->6
-     *     \______/
-     *   In this linked list we can see there is a cycle.
-     *   we can create loop by calling createLoop function in main after creating LL
-     *   createLoop(head,2,5);
-     *  to detect there is loop or not we can call detectloop function in main
-     *  detectloop(head);
+    /**
+     * Creates a loop in a linked list by connecting the next pointer of a node
+     * at a specified starting position (position2) to another node at a specified
+     * destination position (position1). If either position is invalid, no loop
+     * will be created.
+     *
+     * @param head the head node of the linked list
+     * @param position1 the position in the list where the loop should end
+     * @param position2 the position in the list where the loop should start
      */
-
     static void createLoop(Node head, int position1, int position2) {
         if (position1 == 0 || position2 == 0) {
             return;
@@ -39,29 +49,32 @@ static void createLoop(Node head, int position1, int position2) {
 
         int count1 = 1;
         int count2 = 1;
-        // Traverse to find node at position1
+        // Traverse to the node at position1
         while (count1 < position1 && node1 != null) {
             node1 = node1.next;
             count1++;
         }
 
-        // Traverse to find node at position2
+        // Traverse to the node at position2
         while (count2 < position2 && node2 != null) {
             node2 = node2.next;
             count2++;
         }
 
-        // Create a loop by connecting node2's next to node1
+        // If both nodes are valid, create the loop
         if (node1 != null && node2 != null) {
             node2.next = node1;
         }
     }
-    // Method to detect a loop in the linked list
+
     /**
-     * Detects the presence of a loop in the linked list.
+     * Detects the presence of a loop in the linked list using Floyd's cycle-finding
+     * algorithm, also known as the "tortoise and hare" method.
      *
-     * @see <a href="https://en.wikipedia.org/wiki/Cycle_detection#Floyd's_tortoise_and_hare">Floyd's Cycle Detection Algorithm</a>
-     * @return true if loop exists else false
+     * @param head the head node of the linked list
+     * @return true if a loop is detected, false otherwise
+     * @see <a href="https://en.wikipedia.org/wiki/Cycle_detection#Floyd's_tortoise_and_hare">
+     *     Floyd's Cycle Detection Algorithm</a>
      */
     static boolean detectLoop(Node head) {
         Node sptr = head;

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

@@ -12,7 +12,7 @@ public class CreateAndDetectLoopTest {
 
     @BeforeEach
     void setUp() {
-        // Create a linked list: 1 -> 2 -> 3 -> 4 -> 5 -> 6
+        // Set up a linked list: 1 -> 2 -> 3 -> 4 -> 5 -> 6
         head = new CreateAndDetectLoop.Node(1);
         CreateAndDetectLoop.Node second = new CreateAndDetectLoop.Node(2);
         CreateAndDetectLoop.Node third = new CreateAndDetectLoop.Node(3);
@@ -44,7 +44,7 @@ void testCreateAndDetectLoopLoopExists() {
 
     @Test
     void testCreateLoopInvalidPosition() {
-        // Create loop with invalid positions
+        // Create loop with invalid positions (0)
         CreateAndDetectLoop.createLoop(head, 0, 0);
 
         // Ensure no loop was created
@@ -62,10 +62,25 @@ void testCreateLoopSelfLoop() {
 
     @Test
     void testCreateLoopNoChangeForNonExistentPositions() {
-        // Create a loop with positions that don't exist in the linked list
+        // Create a loop with non-existent positions
         CreateAndDetectLoop.createLoop(head, 10, 20);
 
         // Ensure no loop was created
         assertFalse(CreateAndDetectLoop.detectLoop(head), "No loop should be created if positions are out of bounds.");
     }
+
+    @Test
+    void testMultipleNodesWithNoLoop() {
+        // Multiple nodes without creating any loop
+        assertFalse(CreateAndDetectLoop.detectLoop(head), "No loop should be detected for a standard linear list.");
+    }
+
+    @Test
+    void testHeadToTailLoop() {
+        // Create a loop from the tail back to the head
+        CreateAndDetectLoop.createLoop(head, 1, 6);
+
+        // Detect the head-to-tail loop
+        assertTrue(CreateAndDetectLoop.detectLoop(head), "A head-to-tail loop should be detected.");
+    }
 }