线索二叉树实例（前序创建，中序遍历）--2018.5.15

#include <stdio.h>
#include <stdlib.h>

typedef enum
{
    Link,
    Tread
}PointerTag;

typedef char TElemType;

typedef struct TreeNode
{
    TElemType data;  //数据单元

    struct TreeNode *pLChild, *pRChild;  //左右孩子指针
    PointerTag LTag, RTag;  //左右标志 ==0：孩子指针；==1：前后驱
}TreeNode, Tree;

TreeNode *gPre = NULL;

/* 先序创建二叉树 */
void CreateTree(Tree **_t)
{
    TElemType ch = -1;

    scanf("%c", &ch);

    if(ch == '#')
        *_t = NULL;
    else
    {
        *_t = (Tree*)malloc(sizeof(TreeNode));
        if(*_t == NULL)
            return;
        (*_t)->data = ch;
        (*_t)->LTag = Link;
        (*_t)->RTag = Link;
        CreateTree(&((*_t)->pLChild));
        CreateTree(&((*_t)->pRChild));
    }
}

/* 遍历二叉树 */
int InOrderThraverse_Thr(Tree *_t)
{
    Tree *p =NULL;

    p = _t->pLChild;
    while(p != _t)
    {
        while(p->LTag == Link)
            p = p->pLChild;

        printf("%c ", p->data);    //对节点的操作

        while((p->RTag == Tread) && (p->pRChild != _t))
        {
            p = p->pRChild;
            
            printf("%c ", p->data);
        }
        p = p->pRChild;
    }

    return 0;
}

void InOrderThreading(Tree *_p)
{
    if(_p)
    {
        InOrderThreading(_p->pLChild);    //左树线索初始化
        if(!_p->pLChild)    //前驱线索
        {
            _p->LTag = Tread;
            _p->pLChild = gPre;
        }
        if(!gPre->pRChild)  //后继线索
        {
            gPre->RTag = Tread;
            gPre->pRChild = _p;
        }
        gPre = _p;

        InOrderThreading(_p->pRChild);    //右子树线索初始化
    }
}

/* 线索化二叉树 */
int InOrderThread_Head(Tree **_h, Tree *_t)
{
    (*_h) = (TreeNode *)malloc(sizeof(TreeNode));
    if(*_h == NULL)
        return -1;
    
    (*_h)->pRChild = *_h;
    (*_h)->RTag = Link;

    if(!_t)
    {
        (*_h)->pLChild = *_h;
        (*_h)->LTag = Link;
    }
    else
    {
        gPre = *_h;
        (*_h)->LTag = Link;
        (*_h)->pLChild = _t;
        InOrderThreading(_t);
        gPre->pRChild = *_h;
        gPre->RTag = Tread;
        (*_h)->pRChild = gPre;
    }

    return 0;
}

int main(void)
{
    Tree *t=NULL, *temp=NULL;

    printf("请输入前序二叉树的内容：\n");
    CreateTree(&t);
    InOrderThread_Head(&temp, t);       //加入头结点，并线索化  
    printf("输出中序二叉树的内容:\n");  
    InOrderThraverse_Thr(temp);  
                   
    printf("\n");
    return 0;
}

mrrs@ubuntu:~/Desktop/DSC$ ./test
请输入前序二叉树的内容：
ABDG##H###CE#I##F##
输出中序二叉树的内容:
G D H B A E I C F