线索二叉树的基本操作 C语言

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

typedef char elemType;

typedef struct BiTNode
{
    elemType data;
    struct BiTNode *lchild, *rchild;
    int LTag, RTag;
}BiThreadNode, *BiThreadTree;

BiThreadNode * pre;                           //当前访问节点的前驱

//输出元素x
void visit(elemType x)
{
    printf("%c, ", x);
}

//先序输入节点的值，构造二叉树
BiThreadTree createBiThreadTree()
{
    BiThreadNode * T;
    char ch;

    if ((ch = getchar()) == '#')
        T = NULL;
    else
    {
        T = (BiThreadNode *)malloc(sizeof(BiThreadNode));
        T->data = ch;
        T->lchild = createBiThreadTree();
        T->rchild = createBiThreadTree();
    }

    return T;
}

//中序遍历线索化
void InThreading(BiThreadTree T)
{
    if (T != NULL)
    {
        InThreading(T->lchild); //线索化左子树

        if (T->lchild == NULL)  //左孩子为空，则lchild指向前驱pre
        {
            T->LTag = 1;
            T->lchild = pre;
        }
        else T->LTag = 0;

        if (pre->rchild == NULL)    //前驱pre右孩子为空，则当前节点为前驱pre的后继
        {
            pre->RTag = 1;
            pre->rchild = T;
        }
        else pre->RTag = 0;

        pre = T;
        InThreading(T->rchild); //线索化右子树
    }
}

//创建中序线索二叉树
BiThreadNode *CreateInThrTree(BiThreadTree T)
{
    BiThreadNode * ThrHead;   //中序线索二叉树头节点（非根节点）
    /*
     * 设中序遍历第一个节点、最后一个节点分别为first、last
     * 则：first->lchild指向ThrHead
     *     last->rchild指向ThrHead
     *     ThrHead->lchild：指向根节点
     *     ThrHead->rchild：指向last
    */

    ThrHead = (BiThreadNode *)malloc(sizeof(BiThreadNode));
    ThrHead->RTag = 1;
    ThrHead->rchild = ThrHead;  //先将ThrHead->rchild指向自身
    ThrHead->LTag = 0;

    if (T == NULL) ThrHead->lchild = ThrHead;   //若根节点为空，则ThrHead->lchild指向自身
    else
    {
        ThrHead->lchild = T;
        pre = ThrHead;        //将ThrHead赋给pre，pre为中序线索树中first节点前驱
        InThreading(T);       //二叉树线索化完毕，pre指向last节点
        pre->rchild = ThrHead;  //将ThrHead作为last节点后继
        pre->RTag = 1;
        ThrHead->rchild = pre;  //将ThrHead->rchild指向pre(last)
    }

    return ThrHead;
}

//遍历中序线索二叉树
void ThrInOrderTraverse(BiThreadTree ThrHead)
{
    BiThreadNode * temp = ThrHead->lchild;          //让temp指向根节点

    while (temp != ThrHead)
    {
        while (temp->LTag == 0) temp = temp->lchild;    //向左走到尽头
        visit(temp->data);
        while (temp->RTag == 1 && temp->rchild != ThrHead)
        {   //若当前节点无右子树且后继不是头节点，则输出后继的值
            temp = temp->rchild;
            visit(temp->data);
        }
        temp = temp->rchild;                        //遍历右子树
    }
}

int main()
{
    BiThreadTree root;

    printf("请按先序顺序输入节点值，输入‘#’代表节点为空：\n");
    root = createBiThreadTree();
    BiThreadNode * ThrHead = CreateInThrTree(root);
    ThrInOrderTraverse(ThrHead);
    printf("\n");

    return 0;
}