再谈奶牛问题

在博客园上看到很多人讨论的”在csdn上看到奶牛问题，写了下算法“和“奶牛问题”，觉得好玩，自己尝试着用面向对象的方法算了一下，练练手，没有技术含量，记录下来。
一、问题还原
一只刚出生的小牛，4年后生一只小牛，以后每年生一只。现有一只刚出生的小牛，问20年后共有牛多少只？

ps：看到很多人在原题处留言说这题出的不严谨云云。下面的所有实现都是在理想状态下，特此声明。
二、具体实现
1、奶牛实体类

  public class Cow
    {

        public Cow()
        {

        }

        public Cow(int age, int generation, int id, int parentId)
        {
            this.Age = age;
            this.Generation = generation;
            this.Id = id;
            this.ParentId = parentId;
        }

        /// <summary>
        /// 岁数
        /// </summary>
        public int Age { get; set; }

        /// <summary>
        /// 第几代
        /// </summary>
        public int Generation { get; set; }

        /// <summary>
        /// 唯一标识 id
        /// </summary>
        public int Id { get; set; }

        /// <summary>
        /// 母亲id
        /// </summary>
        public int ParentId { get; set; }
    }

 2、生奶牛方法（非递归）

        static List<Cow> listCows = new List<Cow>();
        public static void GetBirth(int year)
        {
            List<Cow> listBornCows = new List<Cow>();//用于添加新生的奶牛
            Cow firstCow = new Cow(1, 1, 1, 0);
            listCows.Add(firstCow);
            for (int i = 0; i < year; i++)
            {
                foreach (Cow item in listCows)
                {
                    item.Age++; //年龄自增
                    if (item.Age > 4)
                    {
                        //生出一头牛
                        Cow birth = new Cow(1, item.Generation + 1, listCows.Count + 1, item.Id);
                        listBornCows.Add(birth); //添加新生的奶牛
                    }
                }
                listCows.AddRange(listBornCows);
                listBornCows.Clear();
            }
        }

 3、输出
下面的显示是按照母亲id来显示结果的，您也可以改成按照第几代或者岁数显示。

        public static List<Cow> GetCowByParentId(int parentId)
        {
            List<Cow> result = new List<Cow>();
            foreach (Cow item in listCows)
            {
                if (item.ParentId == parentId)
                {
                    result.Add(item);
                }
            }
            return result;
        }

        public static void ShowCows()
        {
            int count = 0;
            if (listCows != null)
            {
                count = listCows.Count;
            }
            Console.WriteLine(string.Format("After 20 years,cows count:{0}", count.ToString()));

            /*下面按照所属母亲(ParentId)显示对应奶牛数*/
            int maxParentId = 0;
            if (listCows.Count > 0)
            {
                //按照所属母亲 逆序排序
                listCows.Sort(delegate(Cow left, Cow right) { return right.ParentId.CompareTo(left.ParentId); });
                maxParentId = listCows[0].ParentId;
            }
            for (int i = 0; i < maxParentId; i++)
            {
                List<Cow> listModels = GetCowByParentId(i);
                Console.WriteLine(string.Format("Cow_{0}'s children as follows:", i));
                if (listModels.Count == 0)
                {
                    Console.WriteLine("Has no any child!");
                }
                else
                {
                    foreach (Cow item in listModels)
                    {
                        Console.WriteLine(string.Format("Age:{0},Id:{1},Generation:{2}", item.Age, item.Id, item.Generation));
                    }
                }
            }
        }

 最后贴一下完整代码：

   class Program
    {
        static List<Cow> listCows = new List<Cow>();
        static int maxYear = 20;
        public static void GetBirth(int year)
        {
            List<Cow> listBornCows = new List<Cow>();//用于添加新生的奶牛
            Cow firstCow = new Cow(1, 1, 1, 0);
            listCows.Add(firstCow);
            for (int i = 0; i < year; i++)
            {
                foreach (Cow item in listCows)
                {
                    item.Age++; //年龄自增
                    if (item.Age > 4)
                    {
                        //生出一头牛
                        Cow birth = new Cow(1, item.Generation + 1, listCows.Count + 1, item.Id);
                        listBornCows.Add(birth); //添加新生的奶牛
                    }
                }
                listCows.AddRange(listBornCows);
                listBornCows.Clear();
            }
        }

        public static List<Cow> GetCowByParentId(int parentId)
        {
            List<Cow> result = new List<Cow>();
            foreach (Cow item in listCows)
            {
                if (item.ParentId == parentId)
                {
                    result.Add(item);
                }
            }
            return result;
        }

        public static void ShowCows()
        {
            int count = 0;
            if (listCows != null)
            {
                count = listCows.Count;
            }
            Console.WriteLine(string.Format("After 20 years,cows count:{0}", count.ToString()));

            /*下面按照所属母亲(ParentId)显示对应奶牛数*/
            int maxParentId = 0;
            if (listCows.Count > 0)
            {
                //按照所属母亲 逆序排序
                listCows.Sort(delegate(Cow left, Cow right) { return right.ParentId.CompareTo(left.ParentId); });
                maxParentId = listCows[0].ParentId;
            }
            for (int i = 0; i < maxParentId; i++)
            {
                List<Cow> listModels = GetCowByParentId(i);
                Console.WriteLine(string.Format("Cow_{0}'s children as follows:", i));
                if (listModels.Count == 0)
                {
                    Console.WriteLine("Has no any child!");
                }
                else
                {
                    foreach (Cow item in listModels)
                    {
                        Console.WriteLine(string.Format("Age:{0},Id:{1},Generation:{2}", item.Age, item.Id, item.Generation));
                    }
                }
            }
        }

        static void Main(string[] args)
        {
            GetBirth(maxYear);
            ShowCows();
            Console.ReadLine();
        }
    }