C# 上機題的 OO 實作：策略模式

前陣子看到某人《關於某道 C# 上機題的 OO》，後來又有人用裝飾模式做這題，這裡我來個策略模式。不習慣廢話，直接上程式碼，不知道算不算策略模式，請高人指點。

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp
{
    public class Program
    {
        static void Main(string[] args)
        {
            Game game = new Game(17);
            // 設定策略
            game.Strategy = new StrategyA();
            game.GameOver += new EventHandler(game_GameOver);
            game.Start();
            Console.Read();
        }

        static void game_GameOver(object sender, EventArgs e)
        {
            Console.WriteLine("Last Person:" + sender);
        }
    }

    /// 
策略介面
    public interface IStrategy
    {
        /// 
執行策略
        void Work(Game g);
    }

    /// 
策略 A：從第一個人開始報數，報到 3 的倍數退出，直到剩下最後一人
    public class StrategyA : IStrategy
    {
        private List<Person> over = new List<Person>();
        private int k = 0;

        public void Work(Game game)
        {
            foreach (Person p in game.Players)
            {
                p.Say(++k);
                if (k % 3 == 0) over.Add(p);
            }
            game.Players.RemoveAll(o => over.Contains(o));
        }
    }

    public delegate void EventHandler(object sender, EventArgs e);

    /// 
遊戲
    public class Game
    {
        public Game(int num)
        {
            Players = new List<Person>();
            for (int i = 0; i < num; i++) Players.Add(new Person(i + 1));
        }

        public IStrategy Strategy { get; set; }
        public List<Person> Players { get; set; }
        public event EventHandler GameOver;

        public void Start()
        {
            if (Strategy != null)
            {
                while (Players.Count > 1)
                {
                    Strategy.Work(this);
                }
                GameOver(this.Players.First().Id, new EventArgs());
            }
        }
    }

    /// 
玩家
    public class Person
    {
        public Person(int id) { this.Id = id; }
        public int Id { get; set; }

        public void Say(int num)
        {
            Console.WriteLine(string.Format("{0}:{1}", Id, num));
        }
    }
}

StrategyA 實作介面 IStrategy 遵循開閉原則，若要換規則只要新增一個實作 IStrategy 的類別即可。之前還有用循環鏈結串列完成這道題，晚上再發上來。