链表

template <class Elem> 
//单链表
class Link
{
public:
    Elem element;
    Link *next;
    Link(const Elem& elemval,link *nextval=NULL)
    {
        element=elemval; next=nextval;
    }
    Link(Link * nextval=NULL) 
    {
        next=nextval;
    }
};
template <class Elem> 
class LList:public List<Elem>
{
private:
    Link<Elem>* head;
    Link<Elem>* tail;
    Link<Elem>* fence;
    int leftcnt;
    int rightcnt;
    void init()
    {
        fence=tail=head=new Link<Elem>;
        leftcnt=rightcnt=0;
    }
    void removeall()
    {
        while(head!=NULL)
        {
            fence=head;
            head=head->next;
            delete fence;
        }
    }
public:
    LList(int size=DefaultListSize)
    { 
        init();
    }
    ~LList()
    {
        removeall();
    }
    void clear()
    {
        removeall(); init();
    }
    bool insert(const Elem&);
    bool append(const Elem&);
    bool remove(Elem &);
    void setStart()
    {
        fence=head;rightcnt+=leftcnt;leftcnt=0;
    }
    void setEnd()
    {
        fence=tail;leftcnt+=rightcnt;rightcnt=0;
    }
    void prev();
    void next()
    {
        if(fence!=tail)
        {
            fence=fence->next;rightcnt--;leftcnt++;
        }
    }
    int leftLength() const 
    {
        return leftcnt;
    }
    int rightlength const 
    {
        return rightcnt;
    }
    bool setPos(int pos);
    bool getValue(Elem & it) const
    {
        if(rightLength()==0) 
            return false;
        it=fence->next->element;
        return true;
    }
    void print() const;
};

template <class Elem>
bool LList<Elem>::insert(const Elem& item)
{
    fence->next=new Link<Elem>(item,fence->next);
    if(tail==fence) tail=fence->next;
    rightcnt++;
    return true;
}

template <class Elem>
bool LList<Elem>::append(const Elem& item)
{
    tail=tail->next=new Link<Elem>(item,NULL);
    rightcnt++;
    return true;
}

template <class Elem>
bool LList<Elem>::remove(Elem & it)
{
    if(fence->next==NULL) return false;
    it=fence->next->element;
    Link<Elem> *ltemp=fence->next;
    fence->next=ltemp->next;
    if(tail==ltemp) tail=fence;
    delete ltemp;
    rightcnt--;
    return true;
}

template <class Elem>
void LList<Elem>::prev()
{
    Link<Elem> * temp=head;
    if(fence==head) return;
    while(temp->next!=fence) temp=temp->next;
    fence=temp;
    leftcnt--;rightcnt++;
}

template <class Elem>
bool LList<Elem>::setPos(int pos)
{
   if((pos<0)||(pos>rightcnt+leftcnt)) return false;
   fence=head;
   for(int i=0;i<pos;i++)
       fence=fence->next;
   return true;
}
template <class Elem> 
void LList<Elem>::print() const
{
    Link<Elem>* temp=head;
    cout<<"< ";
    while(temp!=fence)
    {
        cout<<temp->next->element<<"";
        temp=temp->next;
    }
    cout<<"| ";
    while(temp->next!=NULL)
    {
        cout<<temp->next->element<<"";
        temp=temp->next;
    }
    cout<<">\n";
}


template <class Elem> 
class DLink                        //双链表的节点表达类
{
private:
    static DLink<Elem> *freelist;
public:
    Elem element;
    DLink *next;
    DLink *prev;
    link(const Elem& e,DLink* prevp=NULL,DLink* nextp=NULL)
    {
        element=e;prev=prevp; next=nextp;
    }
    DLink(DLink *prevp=NULL,DLink* nextp=NULL)
    {
        prev=prevp; next=nextp;
    }
    void *operator new(size_t);
    void operator delete(void*);
};      ////

template <class Elem>
DLink<Elem> *DLink<Elem>::freelist=NULL;

template<class Elem>
void *DLink<Elem>::operator new(size_t)
{
    if(freelist==NULL) return ::new DLink;
    DLink<Elem> *temp=freelist;
    freelist=freelist->next;
    return temp;
}

template<class Elem>
void DLink<Elem>::operator delete(void *ptr)
{
    ((DLink<Elem>*)ptr)->next=freelist;
    freelist(Link<Elem>*ptr);
}


//双链表中某些函数的实现
template <class Elem>
class DList:public list<Elem>
{
private:
    DLink<Elem> *head;
    DLink<Elem> *tail;
    DLink<Elem> *fence;
    int leftcnt;
    int rightcnt;
public:
    bool insert(const Elem&);
    bool append(const Elem&);
    bool remove(Elem&）；
    void prev();
};

template <class Elem>
bool DList<Elem>::insert(const Elem& item)
{
    fence->next=new DLink<Elem>(item,fence,fence->next);
    if(fence->next->next!=NULL)
        fence->next->next->prev=fence->next;
    if(tail==fence)
        tail=fence->next;
    rightcnt++;
    return true;
}

template <class Elem>
bool DList<Elem>::append(const Elem& item)
{
    tail=tail->next=new DLink<Elem>(item,tail,NULL);
    rightcnt++;
    return true;
}

template <class Elem>
bool DList<Elem>::remove(Elem& it)
{
    if(fence->next==NULL) 
        return false;
    it=fence->next->element;
    DLink<Elem>* ltemp=fence->next;
    if(ltemp->next!=NULL) 
        ltemp->next->prev=fence;
    else tail=fence;
    fence->next=ltemp->next;
    delete ltemp;
    rightcnt--;
    return true;
}

template<class Elem>
void DList<Elem>::prev()
{
    if(fence!=head)
    {
        fence=fence->prev;leftcnt--;rightcnt++;
    }
}