Linked List in PHP. Source: https://medium.com/@fazlulkabir94/linked-list-in-php-b677cdb06105

index.php

<?php

$list = new LinkedList();

LinkedList.php

<?php

class LinkedList
{
    private $head;

    public function __construct()
    {
        $this->head = null;
    }

    public function insertAtFront($data): void
    {
        if ($this->head) {
            $newNode = new Node();
            $newNode->setData($data);
            $newNode->setNext($this->head);
            $this->head = $newNode;
        } else {
            $newNode = new Node();
            $newNode->setData($data);
            $this->head = $newNode;
        }
    }

    public function insertBeforeSpecificNode($data, $target): void
    {
        if ($this->head) {
            $currentNode = $this->head;
            $previousNode = null;

            while ($currentNode->getData() != $target && $currentNode->getNext() != null) {
                $previousNode = $currentNode;
                $currentNode = $currentNode->getNext();
            }

            if ($currentNode->getData() == $target) {
                $newNode = new Node();
                $newNode->setData($data);

                if ($previousNode) {
                    $previousNode->setNext($newNode);
                    $newNode->setNext($currentNode);
                } else {
                    $previousNode = $newNode;
                    $previousNode->setNext($currentNode);
                    $this->head = $previousNode;
                }
            }
        }
    }

    public function insetAtBack($data): void
    {
        $newNode = new Node();
        $newNode->setData($data);

        if ($this->head) {
            $currentNode = $this->head;
            while ($currentNode->getNext() != null) {
                $currentNode = $currentNode->getNext();
            }
            $currentNode->setNext($newNode);
        } else {
            $this->head = $newNode;
        }
    }

    public function insertAfterSpecificNode($data, $target): void
    {
        if ($this->head) {
            $currentNode = $this->head;
            while ($currentNode->getData() != $target && $currentNode->getNext() != null) {
                $currentNode = $currentNode->getNext();
            }

            if ($currentNode->getData() == $target) {
                $newNode = new Node();
                $newNode->setData($data);

                $currentNodeNext = $currentNode->getNext();
                $currentNode->setNext($newNode);
                $newNode->setNext($currentNodeNext);
            }
        }
    }

    public function deleteAtFront(): bool
    {
        if ($this->head) {
            $currentNode = $this->head;
            $this->head = $currentNode->getNext();
            unset($currentNode);
            return true;
        }
        return false;
    }

    public function deleteAtBack(): bool
    {
        if ($this->head) {
            $currentNode = $this->head;
            $previousNode = null;
            while ($currentNode->getNext() != null) {
                $previousNode = $currentNode;
                $currentNode = $currentNode->getNext();
            }
            if ($previousNode) {
                unset($currentNode);
                $previousNode->setNext(null);
            } else {
                $this->head = null;
            }
            return true;
        }
        return false;
    }

    public function deleteNode($target): bool
    {
        if ($this->head) {
            $currentNode = $this->head;
            $previousNode = null;

            while ($currentNode->getData() != $target && $currentNode->getNext() != null) {
                $previousNode = $currentNode;
                $currentNode = $currentNode->getNext();
            }

            if ($currentNode->getData() == $target) {
                if ($previousNode) {
                    $previousNode->setNext($currentNode->getNext());
                    unset($currentNode);
                } else {
                    $this->head = $currentNode->getNext();
                    unset($currentNode);
                }
                return true;
            }
        }

        return false;
    }

    public function printNode(): void
    {
        $currentNode = $this->head;
        while ($currentNode != null) {
            echo $currentNode->getData();
            $currentNode = $currentNode->getNext();
            echo " ";
        }
    }
}

Node.php

<?php

class Node
{
    private $data;
    private $next;

    public function __construct()
    {
        $this->data = 0;
        $this->next = null;
    }

    public function getData(): int
    {
        return $this->data;
    }

    public function setData($data): void
    {
        $this->data = $data;
    }

    public function getNext()
    {
        return $this->next;
    }

    public function setNext($next): void
    {
        $this->next = $next;
    }
}