package Test;

 public class Count3Quit1$2 {

     public static void main(String[] args) {

         PeopleCircle pc = new PeopleCircle(500);

         int countNum = 0;

         People del = pc.getLast(); //先把位置指向last,一开始计数就会指向第一个元素

         while(pc.getCount() > 1){

             countNum++;

             del = del.getRight();//跟踪当前的元素位置，且到了末尾会自动从头开始跟踪

             if(countNum == 3){

                 pc.delete(del);

                 countNum = 0;

             }

         }

         System.out.println(pc.getCount());

         System.out.println(pc.getFirst());

         System.out.println(pc.getLast());

     }

 }

 //要求：有一群人围成一圈数数，逢3退1人，要求算出最后留下来的人的下标

 //用面向对象思想，有三个步骤：

 //(1)有哪些类(2)有哪些属性方法(3)类的关系

 //(1)有哪些类？找名词--"有一群人围成一圈",所以有类People,PeopleCircle

 class People{

     private int id;

     private People left;

     private People right;

     public People(int id) {

         super();

         this.id = id;

     }

     public People getLeft() {

         return left;

     }

     public void setLeft(People left) {

         this.left = left;

     }

     public People getRight() {

         return right;

     }

     public void setRight(People right) {

         this.right = right;

     }

     @Override

     public String toString() {

         return "People-"+id;

     }

 }

 class PeopleCircle{

     private int count = 0;

     public int getCount() {

         return count;

     }

     public PeopleCircle(int count) {

         for(int i = 0; i < count ; i++){

             add();

         }

     }

     private People first;

     public People getFirst() {

         return first;

     }

     private People last;

     public People getLast() {

         return last;

     }

     public void add(){

         People p = new People(count);

         if(count <= 0 ){

             p.setLeft(p);

             p.setRight(p);

             first = p;

             last = p;

             count++;

         }else {

             last.setRight(p);

             p.setLeft(last);

             p.setRight(first);

             first.setLeft(p);

             last = p;

             count++;

         }

     }

     public void delete(People p){

         if(count <= 0){

             System.out.println("已经没有人！");

             return;

         }else if(count == 1){

             first = last = null;

             count--;

         }else{

             p.getLeft().setRight(p.getRight());

             p.getRight().setLeft(p.getLeft());

             if(p == first){

                 first = p.getRight();

             }else if (p == last){

                 last = p.getLeft();

             }

             count--;

         }

     }

 }