Add TortoiseHareAlgo implementation with append, toString, and getMiddle methods (TheAlgorithms#6722)

* Create TortoiseHareAlgorithm.java Implement TortoiseHareAlgo with append, getMiddle, and toString methods - Added generic singly linked list with inner Node class - Implemented append() to add elements - Implemented getMiddle() using Tortoise-Hare approach - Added toString() for readable list representation * Create TortoiseHareAlgoTest.java Add JUnit tests for TortoiseHareAlgo - Verified append() and toString() output - Tested getMiddle() for odd, even, and empty lists - Ensured correct behavior and null handling * Update README.md Add TortoiseHareAlgo to linked list documentation - Added TortoiseHareAlgo.java to file descriptions - Described its purpose: finding middle element using Tortoise-Hare algorithm * Rename TortoiseHareAlgorithm.java to TortoiseHareAlgo.java Fixed build error * Update TortoiseHareAlgoTest.java Fixed line formatting build error * Update TortoiseHareAlgoTest.java Fixed line formatting build error * Update TortoiseHareAlgo.java Added {} after if statement instead of directly writing statement * Update TortoiseHareAlgo.java Fixed line formatting build error * Update TortoiseHareAlgo.java Added {} after if statement instead of directly writing statement * Update TortoiseHareAlgoTest.java Replace .* import with specific imports --------- Co-authored-by: Deniz Altunkapan <deniz.altunkapan@outlook.com>

Author: TejasSingh022

src/main/java/com/thealgorithms/datastructures/lists/README.md

@@ -30,3 +30,4 @@ The `next` variable points to the next node in the data structure and value stor
 6. `MergeKSortedLinkedlist.java` : Merges K sorted linked list with mergesort (mergesort is also the most efficient sorting algorithm for linked list).
 7. `RandomNode.java` : Selects a random node from given linked list and diplays it.
 8. `SkipList.java` : Data Structure used for storing a sorted list of elements with help of a Linked list hierarchy that connects to subsequences of elements.
+9. `TortoiseHareAlgo.java` : Finds the middle element of a linked list using the fast and slow pointer (Tortoise-Hare) algorithm.

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

@@ -0,0 +1,63 @@
+package com.thealgorithms.datastructures.lists;
+
+public class TortoiseHareAlgo<E> {
+ static final class Node<E> {
+ Node<E> next;
+ E value;
+
+ private Node(E value, Node<E> next) {
+ this.value = value;
+ this.next = next;
+ }
+ }
+
+ private Node<E> head = null;
+
+ public TortoiseHareAlgo() {
+ head = null;
+ }
+
+ public void append(E value) {
+ Node<E> newNode = new Node<>(value, null);
+ if (head == null) {
+ head = newNode;
+ return;
+ }
+ Node<E> current = head;
+ while (current.next != null) {
+ current = current.next;
+ }
+ current.next = newNode;
+ }
+
+ public E getMiddle() {
+ if (head == null) {
+ return null;
+ }
+
+ Node<E> slow = head;
+ Node<E> fast = head;
+
+ while (fast != null && fast.next != null) {
+ slow = slow.next;
+ fast = fast.next.next;
+ }
+
+ return slow.value;
+ }
+
+ @Override
+ public String toString() {
+ StringBuilder sb = new StringBuilder("[");
+ Node<E> current = head;
+ while (current != null) {
+ sb.append(current.value);
+ if (current.next != null) {
+ sb.append(", ");
+ }
+ current = current.next;
+ }
+ sb.append("]");
+ return sb.toString();
+ }
+}

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

@@ -0,0 +1,46 @@
+package com.thealgorithms.datastructures.lists;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+class TortoiseHareAlgoTest {
+
+ @Test
+ void testAppendAndToString() {
+ TortoiseHareAlgo<Integer> list = new TortoiseHareAlgo<>();
+ list.append(10);
+ list.append(20);
+ list.append(30);
+ assertEquals("[10, 20, 30]", list.toString());
+ }
+
+ @Test
+ void testGetMiddleOdd() {
+ TortoiseHareAlgo<Integer> list = new TortoiseHareAlgo<>();
+ list.append(1);
+ list.append(2);
+ list.append(3);
+ list.append(4);
+ list.append(5);
+ assertEquals(3, list.getMiddle());
+ }
+
+ @Test
+ void testGetMiddleEven() {
+ TortoiseHareAlgo<Integer> list = new TortoiseHareAlgo<>();
+ list.append(1);
+ list.append(2);
+ list.append(3);
+ list.append(4);
+ assertEquals(3, list.getMiddle()); // returns second middle
+ }
+
+ @Test
+ void testEmptyList() {
+ TortoiseHareAlgo<Integer> list = new TortoiseHareAlgo<>();
+ assertNull(list.getMiddle());
+ assertEquals("[]", list.toString());
+ }
+}