Queue.php

<?php
/**
 * A simple queue implementation in PHP
 */
class Queue
{
    private $items = array();
    private $front = 0;
    private $rear = -1;
    private $size = 0;

    /**
     * Add an item to the end of the queue
     * @param mixed $item The item to add to the queue
     */
    public function enqueue($item)
    {
        $this->items[++$this->rear] = $item;
        $this->size++;
    }

    /**
     * Remove and return the item at the front of the queue
     * @return mixed The item at the front of the queue
     */
    public function dequeue()
    {
        if ($this->isEmpty()) {
            return null;
        }
        $item = $this->items[$this->front];
        unset($this->items[$this->front]);
        $this->front++;
        $this->size--;
        return $item;
    }

    /**
     * Get the item at the front of the queue without removing it
     * @return mixed The item at the front of the queue
     */
    public function peek()
    {
        if ($this->isEmpty()) {
            return null;
        }
        return $this->items[$this->front];
    }

    /**
     * Check if the queue is empty
     * @return bool True if the queue is empty, false otherwise
     */
    public function isEmpty()
    {
        return $this->size === 0;
    }

    /**
     * Get the number of items in the queue
     * @return int The number of items in the queue
     */
    public function size()
    {
        return $this->size;
    }

    /**
     * Clear all items from the queue
     */
    public function clear()
    {
        $this->items = array();
        $this->front = 0;
        $this->rear = -1;
        $this->size = 0;
    }
}