#include <iostream>
using namespace std;
class ListHead{
public:
    ListHead *prev,*next;
};
class List{
    
public:
    ListHead *head;
    List()
    {
        head = new ListHead();
        head->prev = head;
        head->next = head;
    }
    ~List()
    {
        delete head;
        head 
 
= NULL;
    }
    void _listAdd(ListHead *toAdd,ListHead*prev,ListHead *next)
    {
        next->prev = toAdd;
        toAdd->next = next;
        toAdd->prev = prev;
        prev->next = toAdd;

    }
    void listAdd(ListHead *toAdd)
    {
        _listAdd(toAdd,head,head->next);
    }
    
 
void listAddTail(ListHead *toAdd)
    {
        _listAdd(toAdd,head->prev,head);
    }
    void _listDelete(ListHead*prev,ListHead *next)
    {
        prev->next = next;
        next->prev = prev;
    }
    void listDelete(ListHead *entry)
    {
        _listDelete(entry->prev,entry->next);
        entry
 
->prev = NULL;
        entry->next = NULL;
    }
    int listEmpty()
    {
        return head->next == head;
    }
};

隊列實現