建立中序线索二叉树

#include <iostream>
#include <stdio.h>

using namespace std;

typedef char TElemType;
enum PointerTag{ Link,Thread };//Link == 0 :指针，Thread == 1 :线索
typedef struct BiThrNode
{
    TElemType data;
    struct BiThrNode *lchild,*rchild;
    PointerTag LTag,RTag;
}BiThrNode,*BiThrPtr;

BiThrPtr pre=NULL;//定义全局变量

//默认按前序遍历的顺序输入，尾结点用#表示
int Create_BiThrTree(BiThrPtr& T)
{
    TElemType c;
    //cout << "请输入当前节点元素值：" << endl;
    cin>>c;
    if(c == '#') T=NULL;
    else
    {
        T = new BiThrNode;
        T->data=c;
        T->LTag=Link;
        T->RTag=Link;
        Create_BiThrTree(T->lchild);
        Create_BiThrTree(T->rchild);
    }
    return 0;
}

//中序遍历输入各节点
int InOrderDisplay(BiThrPtr& T)
{
    if(T)
    {
        InOrderDisplay(T->lchild);
        cout << T->data <<"  ";
        InOrderDisplay(T->rchild);
    }
    return 0;
}


int InOrderTraverse(BiThrPtr& T)
{
    extern BiThrPtr pre;//声明全局变量
    if(T)
    {
        InOrderTraverse(T->lchild);
        if(!T->lchild)
        {
            T->LTag = Thread;
            T->lchild = pre;
        }
        if(!pre->rchild)
        {
            pre->RTag = Thread;
            pre->rchild = T;
        }
        pre = T;
        InOrderTraverse(T->rchild);
    }
    return 0;
}

int InOrderThreading(BiThrPtr p,BiThrPtr& T)
{
    p = new BiThrNode;//额外添加的头结点
    p->data = '#';
    p->LTag = Link;
    p->RTag = Thread;
    p->rchild = p;
    if(!T)
    {
        p->lchild = p;
    }
    else
    {
        p->lchild = T;
        pre = p;
        InOrderTraverse(T);
        pre->RTag = Thread;
        pre->rchild = p;
        p->rchild = pre;
    }
    return 0;
}

int main()
{
    freopen( "input.txt", "r", stdin );//从input.txt中读取输入数据
    BiThrPtr T=NULL,p=NULL;
    Create_BiThrTree(T);//前序遍历创建二叉树
    InOrderDisplay(T);
    InOrderThreading(p,T);
    fclose(stdin);
    return 0;
}

测试数据如下（从txt中读取）：ABC##D##E#F##

思路借鉴小甲鱼视频：http://pan.baidu.com/s/1nv187e5

最上面那个节点是额外添加的头结点