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

代码

   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）

代码

         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。

代码

         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：

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();
        }
    }