A Step-by-Step Guide to Linked Lists in PHP

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A linked list is a dynamic data structure made up of nodes where each node stores data and a pointer (reference) to the next node. Unlike arrays, linked lists do not require contiguous memory allocation, making them flexible for insertion and deletion.

Key Concepts:

Node: A basic building block that contains data and a reference to the next node.
Linked List: A series of nodes where each node points to the next one, forming a chain.

Let’s explore how to implement a linked list in PHP step by step.

Step 1: Create the Node Class

Each node in the linked list contains two parts:

Data: The value stored in the node.
Next: A reference (or pointer) to the next node in the list.

class Node {
public $data;
public $next;

public function __construct($data) {
    $this->data = $data;
    $this->next = null;  // Points to null initially
}

}

Step 2: Create the LinkedList Class

The linked list class manages the nodes. It will have methods to insert nodes and display the list.

class LinkedList {
private $head;

public function __construct() {
    $this->head = null;  // Initially, the list is empty
}

}

Step 3: Insert Nodes

We can insert nodes at the end of the list by traversing the list to find the last node and updating its next pointer to point to the new node.

public function insert($data) {
$newNode = new Node($data);

if ($this->head === null) {
    $this->head = $newNode;  // If the list is empty, the new node becomes the head
} else {
    $current = $this->head;
    while ($current->next !== null) {
        $current = $current->next;  // Traverse to the last node
    }
    $current->next = $newNode;  // Link the last node to the new node
}

}

Step 4: Display the Linked List

To visualize the contents of the list, traverse the list from the head and print each node’s data.

public function display() {
$current = $this->head;
while ($current !== null) {
echo $current->data . " → ";
$current = $current->next;
}
echo “null\n”; // End of the list
}

Step 5: Test the Linked List

Now let’s test the linked list by inserting some data and displaying the results.

$list = new LinkedList();
$list->insert(10);
$list->insert(20);
$list->insert(30);
$list->display();

Output:

10 → 20 → 30 → null

Step 6: Memory Structure

Each node in the linked list is stored at a different memory location, and the next pointer links them together. The last node points to null, signifying the end of the list.

For example:

Node(10) at memory address 0x001 points to Node(20) at 0x002.
Node(20) at memory address 0x002 points to Node(30) at 0x003.
Node(30) at memory address 0x003 points to null.

Conclusion

A linked list in PHP is an efficient data structure for dynamic memory allocation and fast insertions or deletions.

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