Added abstract example of Circular Linked List

Author: Alienpruts

src/Chapter03/CircularLinkedList.php

@@ -0,0 +1,58 @@
+<?php
+/**
+ * Created by PhpStorm.
+ * User: bert
+ * Date: 3/10/18
+ * Time: 9:23
+ */
+
+namespace App\Chapter03;
+
+
+class CircularLinkedList
+{
+    private $_firstNode = NULL;
+    private $_totalNodes = 0;
+
+    /**
+     * Insert new node at end of circular linked list.
+     * We must take care to set the next propery of the inserted node to the first node of the list.
+     * @param string|null $data
+     * @return bool
+     */
+    public function insertAtEnd(string $data = NULL)
+    {
+        $newNode = new ListNode($data);
+        if ($this->_firstNode === NULL){
+            $this->_firstNode = &$newNode;
+        } else {
+            $currenNode = $this->_firstNode;
+            while ($currenNode->next !== $this->_firstNode){
+                $currenNode = $currenNode->next;
+            }
+            $currenNode->next = $newNode;
+        }
+        $newNode->next = $this->_firstNode;
+        $this->_totalNodes++;
+        return true;
+    }
+
+    /**
+     * Display function for a circular linked list.
+     * We cannot use the same method of a normal linked list : we need to take care not to fall into an infinite loop
+     * because of the next property of the last node.
+     */
+    public function display()
+    {
+        echo "Total book titles: " .$this->_totalNodes . PHP_EOL;
+        $currentNode = $this->_firstNode;
+        while ($currentNode->next !== $this->_firstNode){
+            echo $currentNode->data . PHP_EOL;
+        }
+
+        if ($currentNode){
+            echo $currentNode->data . PHP_EOL;
+        }
+    }
+
+}