Algorithms and Data Structures in PHP: A Complete Guide for Beginners

Algorithms and Data Structures in PHP: Where to Start for Beginners

Mastering algorithms and data structures is a key stage in the development of any programmer, including those who have chosen PHP. Many beginners mistakenly believe that for web development, it is enough to know only syntax and frameworks. However, understanding how to efficiently organize and process data directly affects the performance and scalability of your projects. In this article, we will break down basic concepts using practical PHP examples that will help you take the first step into the world of efficient programming.

Why Are Data Structures Important in PHP?

PHP is a dynamically typed language, and its built-in array (array) is actually a hybrid: it can work both as a list and as a dictionary (hash table). This is powerful, but without understanding the underlying structures, you risk writing suboptimal code. For example, searching for an element in an unsorted array of 10,000 records can take 100 times longer than searching in a hash table.

The main structures we will cover:

• Arrays — the foundation, but with nuances.
• Stack and Queue — for tasks with a specific processing order.
• Linked Lists — for dynamic memory management.
• Hash Tables — for fast key-based access.

1. Arrays and Working with Them: From Simple to Complex

In PHP, an array is an ordered mapping that associates keys with values. But even with this universal structure, you can work in different ways.

Indexed and Associative Arrays

An indexed array uses integer keys, while an associative array uses string keys. Example:

<?php// Indexed array$fruits = ["apple", "banana", "cherry"];echo $fruits[1]; // banana

// Associative array (hash table)$user = [    "name" => "Alice",    "age" => 30,    "city" => "Moscow"];echo $user["name"]; // Alice?>

Array Operations

Adding, removing, and searching are basic operations. It is important to know their time complexity:

• array_push() / $arr[] = $val — O(1) on average.
• array_pop() — O(1).
• array_shift() — O(n), as it re-indexes all elements.
• in_array() — O(n) for an unsorted array.
• isset($arr[$key]) — O(1) for associative arrays.

Example of efficiently using an associative array for word frequency counting:

<?php$text = "apple banana apple cherry banana apple";$words = explode(" ", $text);$freq = [];

foreach ($words as $word) {    if (isset($freq[$word])) {        $freq[$word]++;    } else {        $freq[$word] = 1;    }}

print_r($freq);// Array ( [apple] => 3 [banana] => 2 [cherry] => 1 )?>

2. Stack and Queue: LIFO and FIFO Principles in PHP

Stack (Last In, First Out) and Queue (First In, First Out) are classic structures that are easy to implement in PHP using arrays.

Stack Implementation

A stack is used, for example, for checking bracket pairing or undo actions.

<?phpclass Stack {    private array $items = [];

    public function push($item): void {        $this->items[] = $item; // O(1)    }

    public function pop() {        return array_pop($this->items); // O(1)    }

    public function peek() {        return end($this->items); // O(1)    }

    public function isEmpty(): bool {        return empty($this->items);    }}

// Example: checking balanced bracketsfunction isBalanced(string $expr): bool {    $stack = new Stack();    $pairs = [')