Linked List Operations in PHP

Lesson Overview

Welcome to our tutorial focusing on Linked List Operations in PHP. Singly-Linked Lists are among the most fundamental data structures used in computer science. They provide an efficient way to store and access data that is not necessarily contiguous in memory. This ability distinguishes linked lists from arrays, making them an indispensable tool in a programmer's toolkit.

LinkedList Definition

To work with linked lists in PHP, we need to define a ListNode class, which represents a node in the linked list. PHPclass ListNode { public $value; public $next; public function __construct($value) { $this->value = $value; // Holds the value or data of the node $this->next = null; // Points to the next node in the linked list; default is null } } // Initialization of linked list class LinkedListExample { public static function main() { $head = new ListNode(1); $head->next = new ListNode(2); $head->next->next = new ListNode(3); $head->next->next->next = new ListNode(4); $head->next->next->next->next = new ListNode(5); } } In the ListNode class: $value holds the data of the node. $next is a reference to the next node in the linked list. It is null by default, meaning the node does not point to any other node when it's freshly created. To understand this, consider that a linked list is a linear data structure where each element is a separate object known as a node. A node comprises data and a reference (link) to the next node in the sequence. The provided code creates a linked list in which each node points to the next as follows: 1 -> 2 -> 3 -> 4 -> 5, and the last node points to null.

Task Example

O(1)

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PHP

class ListNode {
    public $value;
    public $next;

    public function __construct($value) {
        $this->value = $value;  // Holds the value or data of the node
        $this->next = null;     // Points to the next node in the linked list; default is null
    }
}

// Initialization of linked list
class LinkedListExample {
    public static function main() {
        $head = new ListNode(1);
        $head->next = new ListNode(2);
        $head->next->next = new ListNode(3);
        $head->next->next->next = new ListNode(4);
        $head->next->next->next->next = new ListNode(5);
    }
}

PHP

class ListNode {
    public $value;
    public $next;

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

class ReverseLinkedList {
    public static function reverseLinkedList($head) {
        $prev = null;
        $current = $head;
        while ($current !== null) {
            $nextNode = $current->next;
            $current->next = $prev;
            $prev = $current;
            $current = $nextNode;
        }
        return $prev;
    }

    // Test
    public static function main() {
        $head = new ListNode(1);
        $head->next = new ListNode(2);
        $head->next->next = new ListNode(3);
        $head->next->next->next = new ListNode(4);
        $head->next->next->next->next = new ListNode(5);

        $reversedHead = self::reverseLinkedList($head);
        while ($reversedHead !== null) {
            echo $reversedHead->value . " ";
            $reversedHead = $reversedHead->next;  // Output: 5 4 3 2 1
        }
    }
}

Linked List Operations in PHP

Lesson Overview

LinkedList Definition

Task Example

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