C ＃ output the middle order traversal through the clue binary tree

The procedure is as follows
Build a threaded binary tree , Or to clue binary trees , It's essentially traversing a binary tree . In the process of traversing , The operation of accessing a node is to check the current left , Whether the right pointer field is empty , Change them to clues to the precursor node or the successor node . To achieve this process , Set pointer pre Always point to the node you just visited , If the pointer p Point to the current node , be pre Point to its precursor , To set up clues .
in addition , When adding a cable to a binary tree , You must first apply for a header , Establish the direction relationship between the head node and the root node of the binary tree , After the binary tree is threaded , We also need to establish the clue between the last node and the head node .
The following is a recursive algorithm for building a medium order binary tree , among pre Is a global variable .
///
/// Cue binary tree through middle order traversal
///
///
///
static void InThread(ref ThreadNode p, ref ThreadNode pre)
{
if (p != null)
{
InThread(ref p.lchild,ref pre);
if (p.lchild == null) { p.lchild = pre; p.ltag = 1; }
if (pre!=null&&pre.rchild==null) { pre.rchild = p;pre.rtag = 1; }
pre = p;
InThread(ref p.rchild, ref pre);
}
}
///
/// Create clue binary tree main logic
///
///
static void CreateInThread(ref ThreadNode T) {
ThreadNode pre = null;
if (T!=null) {
InThread(ref T,ref pre);
pre.rchild = null;
pre.rtag = 1;
}

    }
    /// <summary>
    ///  Find the first node of the middle order traversal clue binary tree 
    /// </summary>
    /// <returns></returns>
    static ThreadNode FirstNode(ThreadNode T) {
        while (T.lchild!=null&&T.ltag==0) { T = T.lchild; }
        return T;
    }
    /// <summary>
    ///  Find the nodes in the middle order clue binary tree p Next, the following nodes under the ordered sequence 
    /// </summary>
    /// <param name="p"></param>
    /// <returns></returns>
    static ThreadNode Nextnode(ThreadNode p) {
        if (p.rtag==0) { return FirstNode(p.rchild); }else {
            return p.rchild;
        }
      
    }
    /// <summary>
    ///  The middle order traversal is realized through the middle order clue binary tree 
    /// </summary>
    /// <param name="T"></param>
   static void Inorder(ThreadNode T) {
        for (ThreadNode p=FirstNode(T);p!=null;p=Nextnode(p)) {
            Console.WriteLine(p.data);

        }

    }



}

public class ThreadNode{
public ThreadNode() { }
public int data;// data elements
public ThreadNode lchild, rchild;// Left and right child nodes
public int ltag, rtag;// Left and right cue marks
}

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