6-5 链式表操作集 (20 分)

List Insert(List L, ElementType X, Position P) {
    if(P == L) {
        List q = (List)malloc(sizeof(List));
        q->Data = X;
        q->Next = L;
        return q;
    }

    List q = L;
    while(q) {
        if(q->Next == P) {
            List p = (List)malloc(sizeof(List));
            p->Next = q->Next;
            p->Data = X;
            q->Next = p;
            return L;
        }
        q = q->Next;
    }
    printf("Wrong Position for Insertion\n");
    return ERROR;
}

List Delete(List L, Position P) {
    if(L == P) {
        return L->Next;
    }

    List q = L;
    while(q) {
        if(q->Next == P) {
            q->Next = q->Next->Next;
            return L;
        }
        q = q->Next;
    }
    printf("Wrong Position for Deletion\n");
    return ERROR;
}

Position Find(List L, ElementType X) {
    List q;
    q = L;
    while(q != NULL) {
        if(q->Data == X) {
            return q;
        }
        q = q->Next;
    }
    return ERROR;
}