数据结构–二叉树的线索化

用土办法找到中序前驱

typedef struct BiTNode
{
    ElemType data; //数据域
    struct BiTNode *lchild, *rchild; //左、右孩子指针
    struct BiTnode *parent; //父节点指针
}BiTNode, *BiTree;

BiTNode *p; // p指向目标结点
BiTNode *pre = NULL; //指向当前访问结点的前驱
BiTNode *final = NULL; //用于记录最终结果
void visit(BiTNode* q)
{
    if (p == q)
        final = pre;
    else
        pre = q;
}

void InOrder(BiTree T)
{
    if (T != NULL)
    {
        InOrder(T->lchild);
        visit(T);
        InOrder(T->rchild);
    }
}

中序遍历序列:D G B E A F C

中序线索化

typedef struct ThreadNode
{
    ElemType data;
    struct ThreadNode *lchild, *rchild;
    int ltag, rtag; //左、右线索标志
}ThreadNode, *ThreadTree; 

ThreadNode *pre = NULL; //指向当前访问结点的前驱
void visit(ThreadNode* q)
{
    if (q->lchild != NULL) //左子树为空，建立前驱线索
        q->lchild = pre, q->ltag = 1;
    if (pre != NULL && pre->rchild == NULL) //建立前驱结点的后继线索
        pre->rchild = q, pre->rtag = 1;
    pre = q;
}
void InThread(ThreadTree T)
{
    if (T != NULL)
    {
        InThread(T->lchild);
        visit(T);
        InThread(T->rchild);
    }
}

void CreateInThread(ThreadTree T)
{
    pre = NULL;
    if (T != NULL)
    {
        InThread(T); 
        if (pre->rchild == NULL) //处理遍历的最后一个结点
            pre->rtag = 1; 
    }
}

先序线索化

typedef struct ThreadNode
{
    ElemType data;
    struct ThreadNode *lchild, *rchild;
    int ltag, rtag; //左、右线索标志
}ThreadNode, *ThreadTree; 

ThreadNode *pre = NULL; //指向当前访问结点的前驱
void visit(ThreadNode* q)
{
    if (q->lchild != NULL) //左子树为空，建立前驱线索
        q->lchild = pre, q->ltag = 1;
    if (pre != NULL && pre->rchild == NULL) //建立前驱结点的后继线索
        pre->rchild = q, pre->rtag = 1;
    pre = q;
}
void PreThread(ThreadTree T)
{
    if (T != NULL)
    {
        visit(T);
        if (T->ltag == 0)
            PreThread(T->lchild);
        PreThread(T->rchild);
    }
}

void CreatePreThread(ThreadTree T)
{
    pre = NULL;
    if (T != NULL)
    {
        PreThread(T); 
        if (pre->rchild == NULL) //处理遍历的最后一个结点
            pre->rtag = 1; 
    }
}

后序线索化

typedef struct ThreadNode
{
    ElemType data;
    struct ThreadNode *lchild, *rchild;
    int ltag, rtag; //左、右线索标志
}ThreadNode, *ThreadTree; 

ThreadNode *pre = NULL; //指向当前访问结点的前驱
void visit(ThreadNode* q)
{
    if (q->lchild != NULL) //左子树为空，建立前驱线索
        q->lchild = pre, q->ltag = 1;
    if (pre != NULL && pre->rchild == NULL) //建立前驱结点的后继线索
        pre->rchild = q, pre->rtag = 1;
    pre = q;
}
void PostThread(ThreadTree T)
{
    if (T != NULL)
    {
        PostThread(T->lchild);
        PostThread(T->rchild);
        visit(T);
    }
}

void CreatePostThread(ThreadTree T)
{
    pre = NULL;
    if (T != NULL)
    {
        PostThread(T); 
        if (pre->rchild == NULL) //处理遍历的最后一个结点
            pre->rtag = 1; 
    }
}