数据结构之队列——顺序存储结构（php代码实现——方法三）

<?php
/**
 * 第三种——循环顺序队列的实现方法
 * 此方法是解决前两种方法的缺点，利用循环队列的方法达到了最优时间复杂度和空间复杂度
 *
 *
 */
class SqQueue3{
    const ARR_MAX=20;
    private $SqArr;
    private $front;
    private $rear;

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

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

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

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

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

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

    //从队尾掺入元素
    public function EnQueue($elem){
        $tail=($this->rear + 1)%self::ARR_MAX;//如果此值等于头元素说明队列已满
        if($tail == $this->front){
            return 'ERROR';
        }
        $this->SqArr[$this->rear]=$elem;
        $this->rear=($this->rear+1)%self::ARR_MAX;
        return 'OK';
    }

    //从队头删除元素
    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';
    }

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