PHP 7 Data Structures and Algorithms

Inserting at the first node

When we add a node in the front, or head, we have to consider two simple possibilities. The list can be empty and as a result the new node is the head. This possibility is as simple as it can get. However, if the list already has a head, then we have to do the following:

1. Create the new node.
2. Make the new node as first node or head.
3. Assign the previous head or first node as the next to follow for the newly created first node.

Here is the code for this:

    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; ...