STL list
list 底层维护了一个带头双向循环链表, list的迭代器不像vector、string 的迭代器是原生指针,我们通过将其抽象化,将迭代器封装成一个类,屏蔽其底层实现差异,提供统一的访问方式,使其使用起来像一个指针。
#include <iostream>
#include <algorithm>
#include <assert.h>
namespace my
{
template<class T>
struct __list_node
{
public:
typedef __list_node<T> Node;
__list_node(const T& x = T()) :
_prev(nullptr),
_next(nullptr),
_data(x)
{
}
Node* _prev;
Node* _next;
T _data;
};
template<class T, class Ref, class Ptr>
struct __list_iterator
{
typedef __list_iterator<T, Ref, Ptr> self;
typedef __list_node<T> Node;
Node* _node;
__list_iterator(Node* node) :
_node(node)
{
}
Ref operator*()
{
return _node->_data;
}
Ptr operator->()
{
return &_node->_data;
}
self& operator++()
{
_node = _node->_next;
return *this;
}
self operator++(int)
{
self tmp(*this);
_node = _node->_next;
return tmp;
}
self& operator--()
{
_node = _node->_prev;
return *this;
}
self operator--(int)
{
self tmp(*this);
_node = _node->_prev;
return tmp;
}
bool operator!=(const self& it)
{
return _node != it._node;
}
bool operator==(const self& it)
{
return _node == it._node;
}
};
// ---------------list
template<class T>
class list
{
typedef __list_node<T> Node;
public:
typedef __list_iterator<T, T&, T*> iterator;
typedef __list_iterator<T, const T&, const T*> const_iterator;
iterator begin()
{
return iterator(_head->_next);
}
const_iterator begin() const
{
return const_iterator(_head->_next);
}
iterator end()
{
return iterator(_head);
}
const_iterator end() const
{
return const_iterator(_head);
}
list()
{
_head = new Node();
_head->_next = _head;
_head->_prev = _head;
}
list(const list<T>& li) :
_head(new Node(T()))
{
_head->_next = _head;
_head->_prev = _head;
const_iterator it = li.begin();
while (it != li.end())
{
push_back(*it);
++it;
}
}
~list()
{
clear();
delete _head;
_head = nullptr;
}
void clear()
{
auto it = begin();
while (it != end())
{
it = erase(it);
}
}
iterator insert(iterator pos, const T& x)
{
Node* cur = pos._node;
Node* prev = cur->_prev;
//连接
Node* newNode = new Node(x);
prev->_next = newNode;
newNode->_prev = prev;
newNode->_next = cur;
cur->_prev = newNode;
return iterator(newNode);
}
iterator erase(iterator pos)
{
assert(pos != end());
Node* next = pos._node->_next;
Node* prev = pos._node->_prev;
delete pos._node;
prev->_next = next;
next->_prev = prev;
return iterator(next);
}
bool empty() const
{
return begin() == end();
}
void push_back(const T& x)
{
insert(end(), x);
}
void push_front(const T& x)
{
insert(begin(), x);
}
void pop_front()
{
assert(!empty());
erase(begin());
}
void pop_back()
{
assert(!empty());
/*iterator end = end();
iterator tail = --end;*/
erase(--end());
}
void swap(list<T>& li)
{
std::swap(li._head, _head);
}
void reverse()
{
if (empty())
return;
Node* head = _head->_next;
Node* tail = _head->_prev;
while (head->_prev != tail && head != tail)
{
T tmp = head->_data;
head->_data = tail->_data;
tail->_data = tmp;
head = head->_next;
tail = tail->_prev;
}
}
void print()
{
if (empty())
{
std::cout << "null" << std::endl;
return;
}
iterator it = begin();
while (it != end())
{
std::cout << *it << " ";
it++;
}
std::cout << std::endl;
}
private:
Node* _head;
};
}