Introduction to Queues in PHP | CodeSignal Learn

Introduction to Queues in PHP | CodeSignal Learn

Introduction to Queues

Hello there! Today, we will unveil Queues in coding, likening them to a line in a coffee shop or a queue of print requests. Queues in computer science are First-In, First-Out (FIFO) structures. Consider this example: you're at a theme park — the first person in line for the roller coaster gets on first. Today's lesson revolves around this straightforward yet powerful concept. So, let's dive in!

Implementing a Queue in PHP

Queue Enqueue Operation

Queue Dequeue Operation

Just as enqueue adds an element to our queue, dequeue removes it. It extracts the element at the queue's beginning, reducing its size. However, we encounter an underflow condition if there are no elements to remove. public function dequeue() { if ($this->isEmpty()) // Check if the queue is empty return null; $this->size--; // Decrement size return array_shift($this->queue); // Remove and return the first item } public function isEmpty() { return $this->size == 0; } The dequeue() method checks for emptiness before dispatching the item.

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PHP

public function dequeue() {
    if ($this->isEmpty()) // Check if the queue is empty
        return null;

    $this->size--; // Decrement size
    return array_shift($this->queue); // Remove and return the first item
}

public function isEmpty() {
    return $this->size == 0;
}

Let's explore the implementation of Queues in PHP. An array is ideal for implementing a Queue. Let's define the Queue:

PHP

class Queue {
    private $queue;
    private $size;
    private $capacity;

    public function __construct($capacity) {
        $this->capacity = $capacity;
        $this->queue = [];
        $this->size = 0;
    }

    // Will return true if the Queue is full
    public function isFull() {
        return $this->size == $this->capacity;
    }
}

In the Queue class above, the isFull() method checks if our queue is already at maximum capacity.

Enqueue, a fancy term, denotes adding an item to the queue — the item lines up at the end. Here's how it plays out in our Queue class:

PHP

public function enqueue($item) {
    if ($this->isFull()) // Check if the queue is full
        return;

    array_push($this->queue, $item); // Add item at the end of the array
    $this->size++; // Increment size
}

The enqueue() method checks if our queue has enough space before adding the item.