An explanation of the PHP two-way queue class

(deque, full name double-ended queue) is a data structure with the properties of queue and stack. Elements in a two-way queue can be popped from both ends, and insertion and deletion operations are limited to both ends of the table.

In actual use, there can also be output-limited bidirectional queues (that is, one endpoint allows insertion and deletion, and the other endpoint only allows insertions) and input-limited queues. Bidirectional queue (that is, a bidirectional queue in which one endpoint allows insertion and deletion, and the other endpoint only allows deletion). And if the element inserted from a certain endpoint of the bidirectional queue is restricted to only be deleted from that endpoint, then the bidirectional queue will transform into two adjacent stacks at the bottom.

DEQue.class.php

_type = in_array($type, array(1,2,3,4,5,6))? $type : 1;
        $this->_maxLength = intval($maxlength);
    }
    /** 前端入列
    * @param  Mixed   $data 数据
    * @return boolean
    */
    public function frontAdd($data=null){
        if($this->_type==3){ // 前端输入限制
            return false;
        }
        if(isset($data) && !$this->isFull()){
            array_unshift($this->_queue, $data);
            $this->setAddNum(1);
            return true;
        }
        return false;
    }
    /** 前端出列
    * @return Array
    */
    public function frontRemove(){
        if($this->_type==2){ // 前端输出限制
            return null;
        }
        if(!$this->checkRemove(1)){ // 检查是否依赖输入
            return null;
        }
        $data = null;
        if($this->getLength()>0){
            $data = array_shift($this->_queue);
            $this->setRemoveNum(1);
        }
        return $data;
    }
    /** 后端入列
    * @param  Mixed   $data 数据
    * @return boolean
    */
    public function rearAdd($data=null){
        if($this->_type==5){ // 后端输入限制
            return false;
        }
        if(isset($data) && !$this->isFull()){
            array_push($this->_queue, $data);
            $this->setAddNum(2);
            return true;
        }
        return false;
    }
    /** 后端出列
    * @return Array
    */
    public function rearRemove(){
        if($this->_type==4){ // 后端输出限制
            return null;
        }
        if(!$this->checkRemove(2)){ // 检查是否依赖输入
            return null;
        }
        $data = null;
        if($this->getLength()>0){
            $data = array_pop($this->_queue);
            $this->setRemoveNum(2);
        }
        return $data;
    }
    /** 清空对列
    * @return boolean
    */
    public function clear(){
        $this->_queue = array();
        $this->_frontNum = 0;
        $this->_rearNum = 0;
        return true;
    }
    /** 判断对列是否已满
    * @return boolean
    */
    public function isFull(){
        $bIsFull = false;
        if($this->_maxLength!=0 && $this->_maxLength==$this->getLength()){
            $bIsFull = true;
        }
        return $bIsFull;
    }
    /** 获取当前对列长度
    * @return int
    */
    private function getLength(){
        return count($this->_queue);
    }
    /** 记录入列,输出依赖输入时调用
    * @param int $endpoint 端点 1:front 2:rear
    */
    private function setAddNum($endpoint){
        if($this->_type==6){
            if($endpoint==1){
                $this->_frontNum ++;
            }else{
                $this->_rearNum ++;
            }
        }
    }
    /** 记录出列,输出依赖输入时调用
    * @param int $endpoint 端点 1:front 2:rear
    */
    private function setRemoveNum($endpoint){
        if($this->_type==6){
            if($endpoint==1){
                $this->_frontNum --;
            }else{
                $this->_rearNum --;
            }
        }
    }
    /** 检查是否输出依赖输入
    * @param int $endpoint 端点 1:front 2:rear
    */
    private function checkRemove($endpoint){
        if($this->_type==6){
            if($endpoint==1){
                return $this->_frontNum>0;
            }else{
                return $this->_rearNum>0;
            }
        }
        return true;
    }
} // class end
?>

demo.php

frontAdd('a'); // 前端入列
$obj->rearAdd('b');  // 后端入列
$obj->frontAdd('c'); // 前端入列
$obj->rearAdd('d');  // 后端入列
// 入列后数组应为 cabd
$result = array();
$result[] = $obj->rearRemove(); // 后端出列
$result[] = $obj->rearRemove(); // 后端出列
$result[] = $obj->frontRemove(); // 前端出列
$result[] = $obj->frontRemove(); // 前端出列
print_r($result); // 出列顺序应为 dbca
// 例子2
$obj = new DEQue(3, 5); // 前端只能输出，后端可输入输出，最大长度5
$insert = array();
$insert[] = $obj->rearAdd('a');
$insert[] = $obj->rearAdd('b');
$insert[] = $obj->frontAdd('c'); // 因前端只能输出，因此这里会返回false
$insert[] = $obj->rearAdd('d');
$insert[] = $obj->rearAdd('e');
$insert[] = $obj->rearAdd('f');
$insert[] = $obj->rearAdd('g'); // 超过长度，返回false
var_dump($insert);
// 例子3
$obj = new DEQue(6); // 输出依赖输入
$obj->frontAdd('a');
$obj->frontAdd('b');
$obj->frontAdd('c');
$obj->rearAdd('d');
$result = array();
$result[] = $obj->rearRemove();
$result[] = $obj->rearRemove();  // 因为输出依赖输入，这个会返回NULL
$result[] = $obj->frontRemove();
$result[] = $obj->frontRemove();
$result[] = $obj->frontRemove();
var_dump($result);
?>

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