php implements queue

Queue: Satisfies the first-in-first-out (FIFO) rule;

The following uses PHP to implement a simple circular queue model;

The initial state of the queue, the queue length is 0 , the pointers of the queue head and the queue tail are the same and both are located at the beginning of the queue;

Entering the queue operation: the queue tail pointer moves backward, and the length is increased by one;

Dequeuing operation: the queue head pointer moves to After moving, the length is reduced by one;

Features of circular queue: the queue size is fixed, the memory space opened by the queue can be recycled, the pointer is moved by the remainder operation with queueSize;

The following The example is to use an array to implement queue storage, and the array subscript is used as a pointer;

<?php


/**
 * Class Queue
 */
class Queue
{
    /**
     * @var int 队头指针
     */
    private $_front;

    /**
     * @var int 队尾指针
     */
    private $_rear;

    /**
     * @var array 队列数组
     */
    private $_queue;

    /**
     * @var int 队列实际长度
     */
    private $_queueLength;

    /**
     * @var int 队列容量；
     */
    private $_queueSize;

    /**
     * Queue constructor.初始化队列
     * @param int $capacity 容量（循环队列的最大长度）
     */
    public function __construct($size)
    {
        $this->_queue = [];
        $this->_queueSize = $size;
        $this->_front = 0;
        $this->_rear = 0;
        $this->_queueLength = 0;
    }

    /**
     * 销毁队列；
     */
    public function __destruct()
    {
        unset($this->_queue);
    }

    /**
     * @method 入队
     * @param mixed $elem 入队的元素
     * @return bool
     */
    public function enQueue($elem)
    {
        if (!$this->isFull()) {
            $this->_queue[$this->_rear] = $elem;
            $this->_rear++;
            $this->_rear = $this->_rear % $this->_queueCapacity;
            $this->_queueLength++;
            return true;
        }
        return false;
    }

    /**
     * @method 出队
     * @return mixed|null
     */
    public function deQueue()
    {
        if (!$this->isEmpty()) {
            $elem = $this->_queue[$this->_front];
            //unset($this->_queue[$this->_front]);
            $this->_front++;
            $this->_front %= $this->_queueCapacity;
            $this->_queueLength--;
            return $elem;
        }
        return null;
    }

    /**
     * @method 判断队列是否为空；
     * @return bool
     */
    public function isEmpty()
    {
        return $this->_queueLength === 0;
    }

    /**
     * @method 判断队列是否饱和；
     * @return bool
     */
    public function isFull()
    {
        return $this->_queueLength === $this->_queueCapacity;
    }

    /**
     * @method 遍历队列并输出（测试队列）
     */
    public function outputQueue()
    {
        for ($i = $this->_front; $i < $this->_queueLength + $this->_front; $i++) {
            echo $this->_queue[$i % $this->_queueCapacity].PHP_EOL;
        }
    }

    /**
     * @method 清空队列
     */
    public function clearQueue()
    {
        $this->_queue = [];
        $this->_front = 0;
        $this->_rear = 0;
        $this->_queueLength = 0;
    }
}

Test the queue class. Logically speaking, there is no big problem. Optimization depends on real business scenarios;

$a = new Queue(3);
echo 'enQueue1 $a->enQueue(1)'.PHP_EOL;
$a->enQueue(1);
echo 'enQueue2 $a->enQueue(2)'.PHP_EOL;
$a->enQueue(2);
echo 'enQueue3 $a->enQueue(3)'.PHP_EOL;
$a->enQueue(3);
echo 'enQueue4 $a->enQueue(4)'.PHP_EOL;
$a->enQueue(4);     //讲道理是失败的；
$a->outputQueue();      //输出 1 2 3
echo PHP_EOL;
echo PHP_EOL;
echo $a->deQueue();     //输出 1  队列 2 3
echo PHP_EOL;
echo PHP_EOL;
echo $a->deQueue();     //输出 2  队列 3
$a->enQueue(5);         //队列 3 5
echo PHP_EOL;
echo PHP_EOL;
$a->outputQueue();      //输出 3 5
$a->clearQueue();       //队列空；

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