데이터 구조의 대기 열 ― 순서 저장 구조 (phop 코드 실현 ― 방법 3)

<?php
/**
 *    ――           
 *               ，                         
 *
 *
 */
class SqQueue3{
    const ARR_MAX=20;
    private $SqArr;
    private $front;
    private $rear;

    //     
    public function __construct(){
        $this->SqArr=array();
        $this->front=0;
        $this->rear=0;
    }

    //    
    public function DestroyQueue(){
        $this->SqArr=null;
        $this->front=$this->rear=0;
    }

    //    
    public function ClearQueue(){
        $this->SqArr=array();
        $this->front=$this->rear=0;
    }

    //      
    public function QueueEmpty(){
        if($this->front==$this->rear){
            return 'Null';
        }else{
            return 'No Null';
        }
    }

    //     
    public function QueueLength(){
        return ($this->rear - $this->front + self::ARR_MAX) % self::ARR_MAX;
    }

    //      
    public function GetHead(){
        if($this->rear==$this->front){
            return 'ERROR';
        }
        return $this->SqArr[$this->front];
    }

    //       
    public function EnQueue($elem){
        $tail=($this->rear + 1)%self::ARR_MAX;//               
        if($tail == $this->front){
            return 'ERROR';
        }
        $this->SqArr[$this->rear]=$elem;
        $this->rear=($this->rear+1)%self::ARR_MAX;
        return 'OK';
    }

    //       
    public function DeQueue(){
        if($this->rear==$this->front){
            return 'ERROR';
        }
        unset($this->SqArr[$this->front]);
        $this->front=($this->front + 1)%self::ARR_MAX;
        return 'OK';
    }

    //     
    public function QueueTraverse(){
        $arr=array();
        for($i=0;$i<self::ARR_MAX;$i++){
            if(isset($this->SqArr[$i])){
                $arr[]=$this->SqArr[$i];
            }
        }
        return $arr;
    }
    //  
    public function QueueTraverse2(){
        $arr=array();
        $i=$this->front;
        while($i != $this->rear){
            $arr[]=$this->SqArr[$i];
            $i=($i+1)%self::ARR_MAX;
        }
        return $arr;
    }
}