<?php

class QNode{
    public  $data;
    public  $next;
    public function __construct($data){
        $this->data=$data;
        $this->next=null;
    }
}

class LinkQueue{ //链队列包含头结点,实例化时，此队列为空
    private $data;
    private $next;
    private $front;//指向头结点
    private $rear;//指向尾结点
//    private $length;
    public function __construct(){
        $this->data=null;
        $this->next=null;
        $this->front=$this; //指向头结点
        $this->rear=$this;//指向头结点
//        $this->length=0;
    }

    //销毁队列
    public function DestroyQueue(){
        while($this->front){ //销毁首先是从头结点开始
            $this->rear=$this->front->next;
            unset($this->front);
            $this->front=$this->rear;
        }
    }

    //清空队列
    public function ClearQueue(){
        $p=$this->front->next;
        while($p){
            $q=$p->next;
            unset($p);
            $p=$q;
        }
        $this->front->next=null;
        $this->rear=$this->front;
    }

    //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(){
        $p=$this->front;
        $i=0;
        while($p != $this->rear){
            $i++;
            $p=$p->next;
        }
        return $i;
//        return $this->length;
    }

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

    //从队尾插入元素
    public function EnQueue(){
        $node=new QNode(mt_rand(100,200));
        $node->next=$this->rear->next;
        $this->rear->next=$node;
        $this->rear=$node;
        $this->length++;
    }

    //从队头删除元素
    public function DeQueue(){
        if($this->front==$this->rear){
            return 'ERROR';
        }
        $p=$this->front->next;
        unset($this->front->next);
        $this->front->next=$p->next;

        if($this->rear==$p){ //如果只有一个元素那么，为指针就需要变化了。
            $this->rear=$this->front;
        }
        $this->length--;
        return 'OK';
    }

    //遍历队列元素
    public function QueueTraverse(){
        if($this->front==$this->rear){
            return 'ERROR';
        }

        $arr=array();
        $p=$this->front->next;
        while($p){
            $arr[]=$p->data;
            $p=$p->next;
        }
        return $arr;
    }
}