Added code to insert at first position of a Linked List

Author: Alienpruts

chap-03/linked-lists.php

@@ -18,4 +18,9 @@
 $bookTitles->insert("Programming Intelligence");
 
 // Display data
+$bookTitles->display();
+
+// Insert a new book as the first element of the list.
+$bookTitles->insertAtFirst("Introducing PHP to noobs");
+
 $bookTitles->display();

src/Chapter03/LinkedList.php

@@ -46,4 +46,25 @@ public function display()
         }
     }
 
+    /**
+     * Inserts a node as the first node in the linked list.
+     * We need to take care to set the previous first node as the next value of the inserted node.
+     * @param string|null $data
+     * @return bool
+     */
+    public function insertAtFirst(string $data = NULL)
+    {
+        $newNode = new ListNode($data);
+
+        if ($this->_firstNode === NULL) {
+            $this->_firstNode = &$newNode;
+        } else {
+            $currentFirstNode = $this->_firstNode;
+            $this->_firstNode = &$newNode;
+            $newNode->next = $currentFirstNode;
+        }
+        $this->_totalNodes++;
+        return true;
+    }
+
 }