500个小朋友手拉手围成一个圈，依次按1、2、3报数，报到3的出列，最后一个留在圈里的是第几个？

public class Count3Quit{

    //从数组的角度
    public void m1(){

        boolean[] child = new boolean[500];

        for(int i=0;i<child.length;i++){
            child[i] = true;
        }

        int count = 0;
        int left = child.length;
        int index = 0;

        while(left > 1){
            if(child[index]){
                count++;
            }
            if(count == 3){
                child[index] = false;
                left--;
                count = 0;
            }
            index++;
            if(index == 500){
                index = 0;
            }
        }

        for(int i=0;i<child.length;i++){
            if(child[i]){
                System.out.println(i);
            }
        }
    }

    //从类的角度
    public void m2(){
        Circle circle = new Circle(500);
        Child d = circle.first;
        int num = 0;
        while(circle.count > 1){
            num++;

            if(num == 3){
                circle.delete(d);
                num = 0;
            }
            d = d.right;
        }
        System.out.println(circle.first.index);
    }

        public static void main(String[] args){
        Count3Quit c = new Count3Quit();
        c.m1();
        c.m2();
    }

}

class Circle{

    int count = 0;
    Child first,end;

    public Circle(int num){
        for(int i=0;i<num;i++){
            add();
        }
    }

    void add(){
        Child c = new Child(count);
        if(count == 0){
            c.left = c;
            c.right = c;
            first = c;
            end = c;
        } else{
            c.left = end;
            end.right = c;
            end = c;
            c.right = first;
            first.left = c;
        }
        count++;
    }

    void delete(Child c){
        if(count == 0){
            System.out.println("空空如也");
            return;
        } else if(count == 1){
            first = end = null;
        } else{
            c.left.right = c.right;
            c.right.left = c.left;

            if(c == first){
                first = c.right;
            } else if(c == end){
                end = c.left;
            }
        }
        count --;
    }
}

class Child{

    int index;
    Child left;
    Child right;

    public Child(int index){
        this.index = index;
    }

}

原文地址：https://www.cnblogs.com/yxfyg/p/12342623.html