约瑟夫环 --- 面向对象 --- java代码

package com.kodoyang.Josephus;

/**
 * ---------------------------------------------------------------------
 * 
 * 在罗马人占领乔塔帕特后，39个犹太人与Josephus及他的朋友躲到一个洞中，
 * 39个犹太人决定宁愿死也不要被敌人抓到，于是决定了一个自杀方式，
 * 41个人排成一个圆圈，由第1个人开始报数，每报数到第3人该人就必须自杀，
 * 然后再由下一个重新报数，直到所有人都自杀身亡为止。
 * 然而Josephus和他的朋友并不想遵从，Josephus要他的朋友先假装遵从，
 * 他将朋友与自己安排在第16个与第31个位置，于是逃过了这场死亡游戏。
 * ----------------------------------------------------------------------
 * 
 * 网站上有很多实现了，我提供一种面向对象的实现
 * 把约瑟夫环看成一个正多边形，每个人占据顶点的位置
 * ----------------------------------------------------------------------
 * 
 * 程序的入口类
 * 
 * @author yuki
 *
 */
public class Demo {

    // 程序的入口
    public static void main(String[] args) {
        
        // 一共41个人
        final int N = 41;
        
        // 新建一个具有41条边的正多边形
        Ring r = new Ring(N);
        
        // 记录当前生存的人数
        int i = N;
        // 生存人数为零就结束循环
        while(i != 0){
            // 调用环的报数方法，返回真说明有点死亡，返回假说明无点死亡
            if( r.call() ){
                // 打印当前存活人数
                $("Survival : " + --i);
            }
        }
        
    }
    
    /**
     * 打印语句的封装
     * @param s
     */
    private static void $(String s){
        System.out.println("---------------------------" + s);
    }
    
}

package com.kodoyang.Josephus;
/**
 * 构成环的顶点，它是可以不依赖于环独立存在的
 * 
 * @author yuki
 *
 */
public class Vertex {

    // 唯一标识，会被构造方法初始化
    private int id;
    // 当前点所处的状态
    private boolean dead;
    
    /**
     * 构造方法
     * @param id
     */
    public Vertex(int id){
        this.id = id;
    }

    /**
     * 点被环调用了
     * @param num 环让它报的数
     * @return 
     */
    public void act(int num) {
        // 报数
        System.out.println("id = " + id + ", num = " + num);
        // 如果报的数是2
        if(num == 2){
            // 当前点死亡
            System.out.println("......I am dead......");
            // 设置当前点的死亡状态
            dead = true;
        }
    }

    /**
     * 返回当前点的死亡状态
     * @return
     */
    public boolean isDead() {

        return dead;
    }

}

package com.kodoyang.Josephus;

/**
 * 这是一个报数的环，它由数组实现
 * 在对象实例化的时候确定了点的个数，不在改变
 * 
 * 它由一个个的点拼接而成
 * pos用来记录当前点的位置，num用来记录当前报出的数字
 * 
 * @author yuki
 *
 */
public class Ring {

    // 它由一个个的点拼接而成
    private Vertex[] vers;
    // 记录当前点的位置
    private int pos;
    // 记录当前报出的数字
    private int num;
    
    /**
     * 构造方法
     * @param n 环拥有的节点数
     */
    public Ring(int n){
        // 创建构成环的点的数组
        vers = new Vertex[n];
        // 初始化点的数组
        for(int i = 0; i < vers.length; ++i){
            // 点的构造方法必须接受一个表示点的id的参数
            Vertex ver = new Vertex(i);
            // 把点初始化给数组的第i个位置
            vers[i] = ver;
        }
        // 构造完毕并不能让他马上进入报数状态，所以设报数值为-1
        num = -1;
    }
    
    /**
     * 报数
     * @return 返回true表示有点死亡，否则没有点死亡
     */
    public boolean call(){
        
        // 执行，如果当前的位置不在死亡状态就跳出循环
        do {
            // 获得下一个位置，如果下一个位置是末尾就设为0， 其它情况加1
            pos = pos == vers.length - 1 ? 0 : pos + 1;
        } while( vers[pos].isDead() );
        
        // 获得下一个要报的数，如果下一个位置是2就设为0， 其它情况加1
        num = num == 2 ? 0 : num + 1;
        // 让点报数
        vers[pos].act(num);
        // 当点报出的数为2时，说明报数的点死亡了
        return num == 2;
    }
    
}

id = 1, num = 0
id = 2, num = 1
id = 3, num = 2
......I am dead......
---------------------------Survival : 40
id = 4, num = 0
id = 5, num = 1
id = 6, num = 2
......I am dead......
---------------------------Survival : 39
id = 7, num = 0
id = 8, num = 1
id = 9, num = 2
......I am dead......
---------------------------Survival : 38
id = 10, num = 0
id = 11, num = 1
id = 12, num = 2
......I am dead......
---------------------------Survival : 37
id = 13, num = 0
id = 14, num = 1
id = 15, num = 2
......I am dead......
---------------------------Survival : 36
id = 16, num = 0
id = 17, num = 1
id = 18, num = 2
......I am dead......
---------------------------Survival : 35
id = 19, num = 0
id = 20, num = 1
id = 21, num = 2
......I am dead......
---------------------------Survival : 34
id = 22, num = 0
id = 23, num = 1
id = 24, num = 2
......I am dead......
---------------------------Survival : 33
id = 25, num = 0
id = 26, num = 1
id = 27, num = 2
......I am dead......
---------------------------Survival : 32
id = 28, num = 0
id = 29, num = 1
id = 30, num = 2
......I am dead......
---------------------------Survival : 31
id = 31, num = 0
id = 32, num = 1
id = 33, num = 2
......I am dead......
---------------------------Survival : 30
id = 34, num = 0
id = 35, num = 1
id = 36, num = 2
......I am dead......
---------------------------Survival : 29
id = 37, num = 0
id = 38, num = 1
id = 39, num = 2
......I am dead......
---------------------------Survival : 28
id = 40, num = 0
id = 0, num = 1
id = 1, num = 2
......I am dead......
---------------------------Survival : 27
id = 2, num = 0
id = 4, num = 1
id = 5, num = 2
......I am dead......
---------------------------Survival : 26
id = 7, num = 0
id = 8, num = 1
id = 10, num = 2
......I am dead......
---------------------------Survival : 25
id = 11, num = 0
id = 13, num = 1
id = 14, num = 2
......I am dead......
---------------------------Survival : 24
id = 16, num = 0
id = 17, num = 1
id = 19, num = 2
......I am dead......
---------------------------Survival : 23
id = 20, num = 0
id = 22, num = 1
id = 23, num = 2
......I am dead......
---------------------------Survival : 22
id = 25, num = 0
id = 26, num = 1
id = 28, num = 2
......I am dead......
---------------------------Survival : 21
id = 29, num = 0
id = 31, num = 1
id = 32, num = 2
......I am dead......
---------------------------Survival : 20
id = 34, num = 0
id = 35, num = 1
id = 37, num = 2
......I am dead......
---------------------------Survival : 19
id = 38, num = 0
id = 40, num = 1
id = 0, num = 2
......I am dead......
---------------------------Survival : 18
id = 2, num = 0
id = 4, num = 1
id = 7, num = 2
......I am dead......
---------------------------Survival : 17
id = 8, num = 0
id = 11, num = 1
id = 13, num = 2
......I am dead......
---------------------------Survival : 16
id = 16, num = 0
id = 17, num = 1
id = 20, num = 2
......I am dead......
---------------------------Survival : 15
id = 22, num = 0
id = 25, num = 1
id = 26, num = 2
......I am dead......
---------------------------Survival : 14
id = 29, num = 0
id = 31, num = 1
id = 34, num = 2
......I am dead......
---------------------------Survival : 13
id = 35, num = 0
id = 38, num = 1
id = 40, num = 2
......I am dead......
---------------------------Survival : 12
id = 2, num = 0
id = 4, num = 1
id = 8, num = 2
......I am dead......
---------------------------Survival : 11
id = 11, num = 0
id = 16, num = 1
id = 17, num = 2
......I am dead......
---------------------------Survival : 10
id = 22, num = 0
id = 25, num = 1
id = 29, num = 2
......I am dead......
---------------------------Survival : 9
id = 31, num = 0
id = 35, num = 1
id = 38, num = 2
......I am dead......
---------------------------Survival : 8
id = 2, num = 0
id = 4, num = 1
id = 11, num = 2
......I am dead......
---------------------------Survival : 7
id = 16, num = 0
id = 22, num = 1
id = 25, num = 2
......I am dead......
---------------------------Survival : 6
id = 31, num = 0
id = 35, num = 1
id = 2, num = 2
......I am dead......
---------------------------Survival : 5
id = 4, num = 0
id = 16, num = 1
id = 22, num = 2
......I am dead......
---------------------------Survival : 4
id = 31, num = 0
id = 35, num = 1
id = 4, num = 2
......I am dead......
---------------------------Survival : 3
id = 16, num = 0
id = 31, num = 1
id = 35, num = 2
......I am dead......
---------------------------Survival : 2
id = 16, num = 0
id = 31, num = 1
id = 16, num = 2
......I am dead......
---------------------------Survival : 1
id = 31, num = 0
id = 31, num = 1
id = 31, num = 2
......I am dead......
---------------------------Survival : 0