Queue of data structure--sequential storage structure (PHP code implementation-method two)

<?php/** *  second--non-circular sequential queue implementation method  *  This method, the first implementation method is optimized, the team no longer move elements  *  only change the position of the head pointer  * *  the pros and cons of this method: *   advantages: The time complexity of insertions and deletions are already O (1), High efficiency  *   disadvantage: After the element is deleted, The space above can no longer be exploited, resulting in wasted space  * */class SqQueue2{    private  $SQARR;     private  $front;//point to Team head element     private  $rear;//If the queue is not empty, Then point to the next position of the tail element     //initializes the variable     public function __construct () {         $this->sqarr=array ();          $this->front=0;         $this->rear=0;     }    //Destroy Queue     public function destroyqueue () {          $this->sqarr=null;          $this->front=0;         $this->rear=0;    }    //Empty queue      public function clearqueue () {        $ This->sqarr=array ();         $this->front= $this->rear=0;     }    //determine if the queue is empty     public function  Queueempty () {        if ($this->front== $this->rear) {             return  ' Null ';         }else{            return  ' No null ';        }    }     //get team head element     public function gethead () {         if ($this->front ==  $this->rear) {            return   ' ERROR ';        }         return  $this->sqarr[$this The length of the->front];    }    //queue     public function queuelenghth () {         return  $this->rear-$this->front;    }    //insert elements from the end of the team     public function enqueue ($elem) {          $this->sqarr[$this->rear++]= $elem;     }    //remove elements from Team head      public function dequeue () {        if ($ this->front== $this->rear) {            return   ' ERROR ';    &Nbsp;    }        unset ($this, $this->sqarr[ Front]);         $this->front++;         return  ' OK ';     }    //traversal queue element      Public function queuetraverse () {         $arr =array ();         for ($i = $this->front; $i < $this->rear; $i + +) {              $arr []= $this->sqarr[$i];         }        return  $arr;     }}

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Queue of data structure--sequential storage structure (PHP code implementation-method two)