数据结构---树与二叉树(3)

三、线索二叉树

定义：利用节点子树为空时，指向孩子的链为空值的链来指明节点在某种遍历次序下的前驱和后继结点，就构成线索二叉树。

ThreadTreeNode.cs

using System;

public class ThreadTreeNode
{
    public char data;
    public ThreadTreeNode left,right;
    public int ltag,rtag;
    public ThreadTreeNode(char ch)
    {
        data = ch;   
        left=right=null;
        ltag=rtag=0;
    }
  
   public void preorderChild(ThreadTreeNode p)
   {
      if(p!=null)
      {
         Console.Write(p.data+" ");
         preorderChild(p.left);
         preorderChild(p.right);
      }
   }
}

 

ThreadTree.cs

using System;

public class ThreadTree
{
    public ThreadTreeNode root;
    public static ThreadTreeNode front=null;
    public static int i=0;
    public myStack<char> mq;
    public ThreadTree(string str)
    {
       root = null;
       if(str!=null)
       {
          root=create(str);     
       }
    }

    public ThreadTreeNode create(string str)
    {
        ThreadTreeNode p=null;
        if(str[i]!='.')
        {
           p = new ThreadTreeNode(str[i]);
           i++;
           p.left=create(str);
           p.right=create(str);
        }
        else
          i++; 
       if(p==null)
          Console.WriteLine("返回null");
       else
          Console.WriteLine(p.data+" ");
        return p;
    }

    public void inThreadTree() 
    {
      inThreadTree(root); 
    }
    
    public void inThreadTree(ThreadTreeNode p)
    {
       if(p!=null)
       {
          inThreadTree(p.left);
          if(p.left==null)
          {
              p.ltag=1;
              p.left=front;
          }
          if(p.right==null)
          {
              p.rtag = 1;
          }
          if(front!=null && front.rtag==1)
            front.right=p;
          if(front!=null)
            Console.Write("front= "+ front.data+"  ");
          else 
            Console.Write("front=null ");
          Console.Write("p="+p.data+" ");
          Console.Write("ltag="+p.ltag+" ");
          Console.WriteLine("rtag="+p.rtag+" ");
          
          front = p;
          inThreadTree(p.right);
       }
    }
    
    public ThreadTreeNode innext(ThreadTreeNode p)
    {
          if(p.rtag==1)
           p=p.right;
         else
         {
           p=p.right;
           while(p.ltag==0)
             p=p.left;
         }
         return p;
    }
    //中根遍历线索二叉树
    public void inorder()
    {
         ThreadTreeNode p=root;
         if(p!=null)
         {
           while(p.ltag==0)
               p=p.left;
           do
           {
               Console.Write(p.data+" ");
               p=innext(p);
            }while(p!=null);
          Console.WriteLine();
         }
    }
     
    public ThreadTreeNode inlast(ThreadTreeNode p)
    {
        if(p.ltag==1)
          p=p.left;
        else
        {
          p=p.left;
          while(p.rtag==0)
              p=p.right;
        }
       return p;
    }
    
    public void inorder_last()
    {}
    
    public ThreadTreeNode prenext(ThreadTreeNode p)
    {
        if(p.ltag==0)
        {
          p=p.left;
        }
        else
        {
          if(p.rtag==0)
            p=p.right;
          else
          {
              while(p.rtag==1 && p.right!=null)
                   p=p.right;
               p=p.right;
          }
        }
        return p;
    }
    //先根遍历线索二叉树
    public  void preorder()
    {
        ThreadTreeNode p=root;
         if(p!=null)
         {
             do{
                  Console.Write(p.data+" ");
                  p=prenext(p);
               }while(p!=null);
         }
            Console.WriteLine();
     }
    
    public ThreadTreeNode postlast(ThreadTreeNode p)
    {
         if(p.rtag==0)
            p=p.right;
         else
         {
             while(p.ltag==1 && p.left!=null)
                 p=p.left;
             p=p.left;
         }
         return p;
    }
   
    public void postorder()
    {
         ThreadTreeNode p=root;
         mq = new myStack<char>(20);
         if(p!=null)
         {
             do{
                  //Console.Write(p.data+" ");
                  mq.Push(p.data);
                  p=postlast(p);
               }while(p!=null);
         }
          while(!mq.IsEmpty())
          {
             Console.Write(mq.Pop()+" ");
          }
            Console.WriteLine();
    }

    public void print()  
    {
       root.preorderChild(root);
    }
    
    public static void Main()
    {
        string str = "ABD..EGCF.H#";
        ThreadTree tt = new ThreadTree(str);
        //tt.print();
         tt.inThreadTree();
         tt.inorder();
         tt.preorder();
         tt.postorder();
      }
}

 

因为后跟次序遍历线索二叉树时需要使用到辅助结构栈，myStack见：

http://www.cnblogs.com/kulong995/articles/1436318.html