using System;

namespace Study
{
 /// <summary>
 /// CChain 的摘要说明。
 /// </summary>
 public class CChain
 {
  
  public class CChainNode
  {
   public object Data;
   public CChainNode NextChainNode;
   public CChainNode PreviousChainNode;
   public object Tag;
   public string Key;

   public CChainNode()
   {
    this.Data=null;
    this.Tag=null;
    this.Key=null;
    this.NextChainNode=this.PreviousChainNode=null;
   }

   public CChainNode(object vData,object vTag,string vKey)
   {
    this.Data=vData;
    this.Tag=vTag;
    this.Key=vKey;
    this.NextChainNode=this.PreviousChainNode=null;
   }
  }


  public class CChainIterator
  {
   private CChainNode pCurrentChainNode,pFirstChainNode,pLastChainNode;
   private bool pbFirst,pbLast;

   public CChainIterator(CChainNode vFirstChainNode,CChainNode vLastChainNode)
   {
    this.pCurrentChainNode=this.pFirstChainNode=this.pLastChainNode=null;
    if(vFirstChainNode!=null)
    {
     pCurrentChainNode=pFirstChainNode=vFirstChainNode;
     pbFirst=false;
    }
    if(vLastChainNode!=null)
    {
     pCurrentChainNode=pLastChainNode=vLastChainNode;
     pbLast=false;
    }
   }

   public CChainNode CurrentChainNode
   {
    get
    {
     return this.pCurrentChainNode;
    }
   }
   
   public bool NextChainNode()
   {
    if(this.pFirstChainNode==null)
    {
     return false;
    }
    if(pCurrentChainNode==pFirstChainNode && pbFirst==false)
    {
     pbFirst=true;
     return true;  
    }
    else
    {
     pCurrentChainNode=pCurrentChainNode.NextChainNode;
     if(pCurrentChainNode ==null)
     {
      return false;
     }
     else
     {
      return true;
     }
    }
   }

   public bool PreviousChainNode()
   {
    if(this.pLastChainNode==null)
    {
     return false;
    }
    if(pCurrentChainNode==pLastChainNode && pbLast==false)
    {
     pbLast=true;
     return true;  
    }
    else