CSharp: Iterator Pattern in donet core 3

/// <summary>
/// 迭代器模式 Iterator Pattern
/// geovindu,Geovin Du edit
/// </summary>
public interface IIterator
{
    /// <summary>
    /// Reset to first element
    /// 第一
    /// </summary>
 
    void First();
    /// <summary>
    /// Get next element
    /// 下一个
    /// </summary>
    /// <returns></returns>
    string Next();
    /// <summary>
    /// End of collection check
    /// 是否最生
    /// </summary>
    /// <returns></returns>
    bool IsCollectionEnds();
    /// <summary>
    /// Retrieve Current Item
    /// 是否当前
    /// </summary>
    /// <returns></returns>
    string CurrentItem();
}
 
/// <summary>
///  Science Iterator
///  科学
/// </summary>
public class ScienceIterator : IIterator
{
    /// <summary>
    /// 科目列表
    /// </summary>
    private LinkedList<string> Subjects;
    /// <summary>
    /// 位置
    /// </summary>
    private int position;
    /// <summary>
    ///
    /// </summary>
    /// <param name="subjects">输入科目列表</param>
    public ScienceIterator(LinkedList<string> subjects)
    {
        this.Subjects = subjects;
        position = 0;
    }
    /// <summary>
    /// 第一个位置，0开始
    /// </summary>
    public void First()
    {
        position = 0;
    }
    /// <summary>
    /// 下一个位置，加1
    /// </summary>
    /// <returns></returns>
    public string Next()
    {
        return Subjects.ElementAt(position++);
    }
    /// <summary>
    /// 是否最后
    /// </summary>
    /// <returns></returns>
    public bool IsCollectionEnds()
    {
        if (position < Subjects.Count)
        {
            return false;
        }
        else
        {
            return true;
        }
    }
    /// <summary>
    /// 当前目录
    /// </summary>
    /// <returns></returns>
    public string CurrentItem()
    {
        return Subjects.ElementAt(position);
    }
}
/// <summary>
///  Arts Iterator
///  行为艺术
/// </summary>
public class ArtsIterator : IIterator
{
    /// <summary>
    /// 科目列表
    /// </summary>
    private string[] Subjects;
    /// <summary>
    /// 位置位
    /// </summary>
    private int position;
    /// <summary>
    /// 行位艺术构造对象
    /// </summary>
    /// <param name="subjects">输入科目列表</param>
    public ArtsIterator(string[] subjects)
    {
        this.Subjects = subjects;
        position = 0;
    }
    /// <summary>
    /// 第一
    /// </summary>
    public void First()
    {
        position = 0;
    }
    /// <summary>
    /// 下一个
    /// </summary>
    /// <returns></returns>
    public string Next()
    {
        //Console.WriteLine("Currently pointing to the subject: "+ this.CurrentItem());
        return Subjects[position++];
    }
    /// <summary>
    /// 是否最后
    /// </summary>
    /// <returns></returns>
    public bool IsCollectionEnds()
    {
        if (position >= Subjects.Length)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    /// <summary>
    /// 当前
    /// </summary>
    /// <returns></returns>
    public string CurrentItem()
    {
        return Subjects[position];
    }
}
#endregion
 
#region Aggregate
/// <summary>
///
/// </summary>
public interface ISubjects
{
    IIterator CreateIterator();
}
/// <summary>
/// 科学
/// </summary>
public class Science : ISubjects
{
    /// <summary>
    /// 科目列表
    /// </summary>
    private LinkedList<string> Subjects;
    /// <summary>
    /// 科学构造对象方法
    ///
    /// </summary>
    public Science()
    {
        Subjects = new LinkedList<string>();
        Subjects.AddFirst("Mathematics 应用数学");
        Subjects.AddFirst("Computer Science计算机科学");
        Subjects.AddFirst("Physics物理学");
        Subjects.AddFirst("Electronics电子学");
    }
    /// <summary>
    /// 创建对象
    /// </summary>
    /// <returns></returns>
    public IIterator CreateIterator()
    {
        return new ScienceIterator(Subjects);
    }
}
/// <summary>
/// 行为艺术
/// </summary>
public class Arts : ISubjects
{
    /// <summary>
    /// 科目列表
    /// </summary>
    private string[] Subjects;
    /// <summary>
    /// 构造行为艺术对象
    /// </summary>
    public Arts()
    {
        Subjects = new[] { "English英语", "History历史", "Geography地理", "Psychology心理学" };
    }
    /// <summary>
    /// 创建一个对象方法
    /// </summary>
    /// <returns></returns>
    public IIterator CreateIterator()
    {
        return new ArtsIterator(Subjects);
    }
}

/// <summary>
  /// 迭代器模式 Iterator Pattern
  /// geovindu,Geovin Du edit
  /// </summary>
  /// <typeparam name="T"></typeparam>
  public class Node<T>
  {
      /// <summary>
      ///
      /// </summary>
      ///
      public T Value;
      /// <summary>
      ///
      /// </summary>
      public Node<T> Left, Right;
      /// <summary>
      ///
      /// </summary>
      public Node<T> Parent;
      /// <summary>
      ///
      /// </summary>
      /// <param name="value"></param>
      public Node(T value)
      {
          Value = value;
      }
      /// <summary>
      ///
      /// </summary>
      /// <param name="value"></param>
      /// <param name="left"></param>
      /// <param name="right"></param>
      public Node(T value, Node<T> left, Node<T> right)
      {
          Value = value;
          Left = left;
          Right = right;
 
          left.Parent = right.Parent = this;
      }
  }
  /// <summary>
  ///
  /// </summary>
  /// <typeparam name="T"></typeparam>
  public class InOrderIterator<T>
  {
 
      /// <summary>
      ///
      /// </summary>
      public Node<T> Current { get; set; }
      /// <summary>
      ///
      /// </summary>
      private readonly Node<T> root;
      /// <summary>
      ///
      /// </summary>
      private bool yieldedStart;
      /// <summary>
      ///
      /// </summary>
      /// <param name="root"></param>
      public InOrderIterator(Node<T> root)
      {
          this.root = Current = root;
          while (Current.Left != null)
              Current = Current.Left;
      }
      /// <summary>
      ///
      /// </summary>
      public void Reset()
      {
          Current = root;
          yieldedStart = true;
      }
      /// <summary>
      ///
      /// </summary>
      /// <returns></returns>
      public bool MoveNext()
      {
          if (!yieldedStart)
          {
              yieldedStart = true;
              return true;
          }
 
          if (Current.Right != null)
          {
              Current = Current.Right;
              while (Current.Left != null)
                  Current = Current.Left;
              return true;
          }
          else
          {
              var p = Current.Parent;
              while (p != null && Current == p.Right)
              {
                  Current = p;
                  p = p.Parent;
              }
              Current = p;
              return Current != null;
          }
      }
  }
 
  /// <summary>
  ///
  /// </summary>
  /// <typeparam name="T"></typeparam>
  public class BinaryTree<T>
  {
 
      /// <summary>
      ///
      /// </summary>
      private Node<T> root;
      /// <summary>
      ///
      /// </summary>
      /// <param name="root"></param>
      public BinaryTree(Node<T> root)
      {
          this.root = root;
      }
      /// <summary>
      ///
      /// </summary>
      /// <returns></returns>
      public InOrderIterator<T> GetEnumerator()
      {
          return new InOrderIterator<T>(root);
      }
      /// <summary>
      ///
      /// </summary>
      public IEnumerable<Node<T>> NaturalInOrder
      {
          get
          {
              IEnumerable<Node<T>> TraverseInOrder(Node<T> current)
              {
                  if (current.Left != null)
                  {
                      foreach (var left in TraverseInOrder(current.Left))
                          yield return left;
                  }
                  yield return current;
                  if (current.Right != null)
                  {
                      foreach (var right in TraverseInOrder(current.Right))
                          yield return right;
                  }
              }
              foreach (var node in TraverseInOrder(root))
                  yield return node;
          }
      }
  }

/// <summary>
/// 迭代器模式 Iterator Pattern
/// geovindu,Geovin Du edit
/// </summary>
public static class GeovinDuPrint
{
 
    /// <summary>
    /// 打印
    /// </summary>
    /// <param name="iterator"></param>
    public static void Print(IIterator iterator)
    {
        while (!iterator.IsCollectionEnds())
        {
            Console.WriteLine(iterator.Next());
        }
    }
}

 Console.WriteLine("***迭代器模式  Iterator Pattern Demonstration.***");
    //For Science
    ISubjects subjects= new Science();
    IIterator iterator = subjects.CreateIterator();
    Console.WriteLine("\nScience subjects科学课程： :");
    GeovinDuPrint.Print(iterator);
 
    //For Arts
    subjects = new Arts();           
    iterator = subjects.CreateIterator();
    Console.WriteLine("\nArts subjects 艺术课程:");
    GeovinDuPrint.Print(iterator);
    Console.WriteLine();
 
 
    //
    var root = new Node<int>(1,
new Node<int>(2), new Node<int>(3));
 
    // C++ style
    var it = new InOrderIterator<int>(root);
 
    while (it.MoveNext())
    {
        Console.WriteLine(it.Current.Value);
        Console.WriteLine(',');
    }
    Console.WriteLine();
 
    // C# style
    var tree = new BinaryTree<int>(root);
 
    Console.WriteLine(string.Join(",", tree.NaturalInOrder.Select(x => x.Value)));
 
    // duck typing!
    foreach (var node in tree)
        Console.WriteLine(node.Value);
 
 
    Console.ReadLine();

***迭代器模式  Iterator Pattern Demonstration.***
 
Science subjects科学课程： :
Electronics电子学
Physics物理学
Computer Science计算机科学
Mathematics 应用数学
 
Arts subjects 艺术课程:
English英语
History历史
Geography地理
Psychology心理学
 
2
,
1
,
3
,
 
2,1,3
2
1
3