Implementation of Linked List in PHP

Starting to learn data structures

Today I changed the code font I use. Previously I used console which looked good, but today I found a more preferable style Source Code Pro.
Here are two screenshots - it’s quite pleasing!

Now let’s get to the main topic: linked list operations

Node Class

First we need a Node class to store data

<?php

namespace LinkedList;

class Node
{
    /**
     * @var $data integer
     */
    public $data;

    /**
     * Pointer to next node
     *
     * @var $next Node
     */
    public $next;

    public function __construct(int $data = null)
    {
        // Initialize data assignment, can also be assigned via $node->data = X;
        $this->data = $data;
    }
}

Linked List Manager Class (For node operations)

We’ll break down the manager class code into sections due to its length

Head Insertion

As the name suggests, insert at the head
If list is empty, initialize with current node
If not empty, make new node the head

public function insertHead(int $data) : bool
{
    $newNode = new Node($data);
    $newNode->next = $this->head;
    $this->head = $newNode;

    return true;
}

Insert at Position (index=0 is head, returns false for invalid positions)

public function insert(int $index = 0, int $data) : bool
{
    if (is_null($this->head) || $index === 0) {
        return $this->insertHead($data);
    }

    $currNode = $this->head;
    $startIndex = 1;
    
    for ($currIndex = $startIndex; ! is_null($currNode); ++ $currIndex) {
        if ($currIndex === $index) {
            $newNode = new Node($data);
            $newNode->next = $currNode->next;
            $currNode->next = $newNode;
            return true;
        }
        $currNode = $currNode->next;
    }

    return false;
}

Usage example:

<?php
// Autoload code omitted, see github
require __DIR__.'/../vendor/bootstrap.php';

// Instantiate a linked list manager
$manager = new \LinkedList\Manager();
// 8
$manager->insertHead(8);
// 5 8
$manager->insertHead(5);
// 1 5 8
$manager->insertHead(1);
// 1 2 5 8
$manager->insert(1, 2);
// false (insufficient nodes for position 5)
$manager->insert(5, 4);
// 1 2 5 8 9
$manager->insertEnd(9);

// Returns 3
$manager->find(8);

// Result: 1 2 8 9
$manager->delete(2);

Search Operation

Simply traverse the list to find value

public function find(int $data) : int
{
    $currNode = $this->head;
    for ($i = 0; ! is_null($currNode); ++ $i) {
        if ($currNode->data === $data) {
            return $i;
        }
        $currNode = $currNode->next;
    }
    return -1;
}

Delete Operation

public function delete(int $index) : bool
{
    if (is_null($this->head)) {
        return false;
    } elseif ($index === 0) {
        $this->head = $this->head->next;
    }

    $startIndex = 1;
    $currNode = $this->head;

    for ($i = $startIndex; ! is_null($currNode->next); ++ $i) {
        if ($index === $i) {
            $currNode->next = $currNode->next->next;
            break;
        }
        $currNode = $currNode->next;
    }
    return true;
}

End

The code has been hosted on github
Will continue learning data structures (doubly linked lists, trees, etc.) when time permits!