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

typedef struct ThreadNode{
    char data;
    struct ThreadNode *lchild,*rchild ;
    int ltag , rtag ;                    // tag = 0 表示有孩子
}ThreadNode , *ThreadTree ;
//建樹
ThreadTree CreateThreadTree(){
    char ch ;
    scanf("%c",&ch);
    ThreadTree T = NULL;
    if(ch=='#') return NULL;
    else{
        T = (ThreadTree)malloc(sizeof(ThreadNode));
        T->data = ch ;
        T->lchild = T->rchild = NULL ;
        T->ltag = T->rtag = 0 ;
        T->lchild = CreateThreadTree();
        T->rchild = CreateThreadTree();
    }
    return T;
}
//線索化
void InThread(ThreadTree &p , ThreadTree &pre){
    if(p!=NULL){
        InThread(p->lchild,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(p->rchild,pre);
    }
}

void CreateInThreadTree(ThreadTree T){
    ThreadTree pre = NULL ;
    if(T!=NULL){
        InThread(T,pre);
        pre->rchild = NULL ;
        pre->rtag = 1 ;
    }
}
//查詢中序序列下，p的前驅節點
ThreadNode *FirstNode(ThreadNode *p){
    while(p->ltag==0)
        p = p->lchild;
    return p ;
}
//查詢中序序列下，p的後繼節點
ThreadNode *NextNode(ThreadNode *p){
    if(p->rtag==0)
        return FirstNode(p->rchild);
    else return p = p->rchild ;
}
//中序遍歷
void InOrder(ThreadNode *T){
    for(ThreadNode *p = FirstNode(T);p!=NULL ; p = NextNode(p))
        printf("%c->",p->data);
}
//先序的後繼結點
ThreadNode *PreNext(ThreadNode *T){
    ThreadNode *p ;
    if( T->ltag==0 )
        p = T->lchild ;
    else{
        p = T ;
        while ( T->rtag == 1)
            T = T->rchild ;
        p = T->rchild;
    }
    return p ;
}
//後序的前驅結點
ThreadTree PostPre(ThreadTree p){
    ThreadTree q;
    if( p->ltag==0 )
        q = p->lchild ;
    else{
        q = p ;
        while ( p->rtag == 1)
            p = p->rchild ;
        q = p->rchild;
    }
    return q ;
}
int main()
{
    printf("輸入各節點：\n");
    ThreadTree T = CreateThreadTree();
    CreateInThreadTree(T);
    printf("中序線索二叉樹的中序遍歷：\n");
    InOrder(T);
    printf("\n");

    char ch ;
    scanf("%c",&ch);

    ThreadTree p=(ThreadTree)malloc(sizeof(ThreadNode));
    p->data = ch ;

    PostPre(p);
    printf("後繼結點為:%c",p->data);
}