LinkedList.php

<?php

class Node {
	private $data;
	private $next;

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

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

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

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

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

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 " ";
		}
	}
}

$list = new LinkedList();