PHP数3退1面向对象的写法（猴子选大王）

<?php
        //用面向对象的方法写 将猴子选大王实现 同样数3退1
        class Monkey {
                /**
                 * 定义猴子类
                 * 属性  编号 $id   
                 *       左手 $left  表示的当前猴子左边的猴子
                 *       右手 $right 表示的当前猴子右边的猴子
                */
                        public $id;
                        public $left;
                        public $right;
        }
        class Circle{
                /**
                 * 定义圈类
                 * 属性  猴子的总数 $ct   
                 *       开始的猴子 $first
                 *       结束的猴子 $last 
                 */
                public $ct = 0;
                public $first;
                public $last;
                //构造方法创建圈
                //参数是猴子的个数
                function __construct($c){
                        for($i=0;$i<$c;$i++){
                                $this->add();
                        }
                }

                //猴子的添加方法
                function add(){
                        $m = new Monkey();
                        $m->id = $this->ct;
                        if($this->ct==0){
                                $this->first = $m;
                                $this->last = $m;
                                $m->left = $m;
                                $m->right = $m;
                        }else{
                                $this->last->right = $m;
                                $m->left = $this->last;
                                $m->right = $this->first;
                                $this->first->left = $m;
                                $this->last = $m;
                        }
                        $this->ct++;
                }

                //猴子的删除方法
                function del($m){
                        if($this->ct <=0){
                                return;
                        }else if($this->ct == 1){
                       
                                $this->first = $this->last = null;
                        }else{
                                $m->left->right = $m->right;
                                $m->right->left = $m->left;

                                if($m == $this->first){
                                        $this->first = $m->right;
                                }else if($m == $this->last){
                                        $this->last = $m->left;
                                }
                        }
                        $this->ct--;
                }
       
        }
        /*
                这里的代码就是实现让500只猴子围城一圈然后
                数三个退一个就这样直到还剩一个把那猴子的编号打印出来
        */

        $circle = new Circle(500);

        $number = 0;
        $mk = $circle->first;
        while($circle->ct > 1){
                $number++;
                if($number == 3){
                        $number = 0;
                        $circle->del($mk);
                }
                $mk = $mk->right;
        }
        echo $circle->first->id;
?>