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

Author: TejasSingh022

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

@@ -0,0 +1,59 @@
+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();
+    }
+}