迭代器与List

     List是一个容器，在STL库中（标准模板库）。实质上就是一个双向链表，而且这个双向链表是有头的；他有一个空的头结点，插入删除时不用判断表中有无数据，双向循环可以轻易的_head->prev轻松地找到最后一个节点end。

     它使用内置的迭代器来遍历和管理这个容器，迭代器就像指针一样管理着这个空间，重载实现了与指针以一样的++、*、= 、!=等操作符。 下面让我们简单的模拟实现以下吧。

struct ListNode     //双向链表结点{ListNode(const T& data = 0):_next(NULL), _prev(NULL), _data(data){}T _data;ListNode<T>* _next;ListNode<T>* _prev;};

template<class T>class List{typedef ListNode<T> Node;public:typedef  _Iterator<T, T&, T*>  Iterator;typedef _Iterator<T, const T&, const T*> ConstIterator;typedef _ReverseIterator<T, T&, T*> ReverseIterator;typedef _ReverseIterator<T, const T&,const T*> ConstReverseIterator;List():_head(NewNode()){_head->_next = _head;_head->_prev = _head;}~List(){release();delete _head;}Node* NewNode(const T& x){return new Node(x);}Node* NewNode(){return new Node();}void PushBack(const T& x)   //尾插{Node* tail = _head->_prev;Node* tmp = NewNode(x);tail->_next = tmp;tmp->_prev = tail;tmp->_next = _head;_head->_prev = tmp;}Iterator Begin()  //定义返回迭代器类型的Begin()和End()  {return Iterator(_head->_next);}Iterator End(){return Iterator(_head);}ConstIterator Begin()const {return ConstIterator(_head->_next);}ConstIterator End()const{return ConstIterator(_head);}ReverseIterator rBegin()     //定义返回迭代器类型的rBegin()和rEnd(){return ReverseIterator(_head->_prev);}ReverseIterator rEnd(){return ReverseIterator(_head);}ConstReverseIterator rBegin()const{return ConstReverseIterator(_head->_prev);}ConstReverseIterator rEnd()const{return ConstReverseIterator(_head);}void release(){Node* tmp = _head->_next;while (tmp != _head){Node* del = tmp;tmp = tmp->_next;delete del;}}Iterator Erase(Iterator it){Node* prev = it._node->_prev;Node* next = it._node->_next;delete it._node;prev->_next = next;next->_prev = prev;return  prev;}void PopBack(){Erase(_head->_prev);}void remove(int pos){Iterator it = Begin();while (it != End()){if (pos == 1)it = Erase(it);++it;--pos;}}protected:Node* _head;};

    List实现了尾删和尾插还有随机位置的删除

#include using namespace std;templatestruct ListNode{ListNode(const T& data = 0):_next(NULL), _prev(NULL), _data(data){}T _data;ListNode* _next;ListNode* _prev;};templatestruct _Iterator{typedef ListNode Node;typedef _Iterator Self;_Iterator(Node* node):_node(node){}Ref operator*(){return _node->_data;}Self& operator++(){_node = _node->_next;return *this;}bool operator!=(const Self& other)const{return other._node != _node;}Node* _node;};templatestruct _ReverseIterator{typedef ListNode Node;typedef _Iterator Self;_ReverseIterator(Node* node):_node(node){}Ref operator*(){return _node->_data;}Self& operator++(){_node = _node->_prev;return *this;}bool operator!=(const Self& other)const{return other._node != _node;}Node* _node;};templateclass List{typedef ListNode Node;public:typedef  _Iterator  Iterator;typedef _Iterator ConstIterator;typedef _ReverseIterator ReverseIterator;typedef _ReverseIterator ConstReverseIterator;List():_head(NewNode()){_head->_next = _head;_head->_prev = _head;}~List(){release();delete _head;}Node* NewNode(const T& x){return new Node(x);}Node* NewNode(){return new Node();}void PushBack(const T& x)   //尾插{Node* tail = _head->_prev;Node* tmp = NewNode(x);tail->_next = tmp;tmp->_prev = tail;tmp->_next = _head;_head->_prev = tmp;}Iterator Begin()  //定义返回迭代器类型的Begin()和End()  {return Iterator(_head->_next);}Iterator End(){return Iterator(_head);}ConstIterator Begin()const {return ConstIterator(_head->_next);}ConstIterator End()const{return ConstIterator(_head);}ReverseIterator rBegin()     //定义返回迭代器类型的rBegin()和rEnd(){return ReverseIterator(_head->_prev);}ReverseIterator rEnd(){return ReverseIterator(_head);}ConstReverseIterator rBegin()const{return ConstReverseIterator(_head->_prev);}ConstReverseIterator rEnd()const{return ConstReverseIterator(_head);}void release(){Node* tmp = _head->_next;while (tmp != _head){Node* del = tmp;tmp = tmp->_next;delete del;}}Iterator Erase(Iterator it){Node* prev = it._node->_prev;Node* next = it._node->_next;delete it._node;prev->_next = next;next->_prev = prev;return  prev;}void PopBack(){Erase(_head->_prev);}void remove(int pos){Iterator it = Begin();while (it != End()){if (pos == 1)it = Erase(it);++it;--pos;}}protected:Node* _head;};