一、 list的介绍
- list是可以在常数范围内在任意位置进行插入和删除的序列式容器,并且该容器可以前后双向迭代。
- list的底层是双向链表结构,双向链表中每个元素存储在互不相关的独立节点中,在节点中通过指针指向其前一个元素和后一个元素。
- list与forward_list非常相似:最主要的不同在于forward_list是单链表,只能朝前迭代,已让其更简单高效。
- 与其他的序列式容器相比(array,vector,deque),list通常在任意位置进行插入、移除元素的执行效率更好。
- 与其他序列式容器相比,list和forward_list最大的缺陷是不支持任意位置的随机访问,比如:要访问list的第6个元素,必须从已知的位置(比如头部或者尾部)迭代到该位置,在这段位置上迭代需要线性的时间开销;list还需要一些额外的空间,以保存每个节点的相关联信息(对于存储类型较小元素的大list来说这可能是一个重要的因素)
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二、list的模拟实现
1、list的节点
template<class T>
struct list_node
{
T _data;
list_node<T>* _prev;
list_node<T>* _next;
list_node(const T& x = T())
:_data(x)
, _next(nullptr)
, _prev(nullptr)
{}
};
2、list 的迭代器
template<class T, class Ref, class Ptr>
struct __list_iterator
{
typedef list_node<T> Node;
typedef __list_iterator<T, Ref, Ptr> self;
Node* _node;
__list_iterator(Node* node)
:_node(node)
{}
self& operator++()
{
_node = _node->_next;
return *this;
}
self& operator--()
{
_node = _node->_prev;
return *this;
}
self operator++(int)
{
self tmp(*this);
_node = _node->_next;
return tmp;
}
self operator--(int)
{
self tmp(*this);
_node = _node->_prev;
return tmp;
}
Ref operator*()
{
return _node->_data;
}
Ptr operator->()
{
return &_node->_data;
}
bool operator!=(const self& s)
{
return _node != s._node;
}
bool operator==(const self& s)
{
return _node == s._node;
}
};
3、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 _head->_next;
}
iterator end()
{
return _head;
}
const_iterator begin() const
{
return _head->_next;
}
const_iterator end() const
{
return _head;
}
void empty_init()
{
_head = new Node;
_head->_next = _head;
_head->_prev = _head;
_size = 0;
}
list()
{
empty_init();
}
list(list<T>& lt)
{
empty_init();
for (auto e : lt)
{
push_back(e);
}
}
list<T>& operator=(list<T> lt)
{
swap(lt);
return *this;
}
void swap(list<T> lt)
{
std::swap(_size, lt._size);
std::swap(_head, lt._head);
}
iterator insert(iterator pos, const T& x)
{
Node* cur = pos._node;
Node* newnode = new Node(x);
Node* prev = cur->_prev;
prev->_next = newnode;
newnode->_prev = prev;
newnode->_next = cur;
cur->_prev = newnode;
++_size;
return iterator(newnode);
}
iterator erase(iterator pos)
{
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* next = cur->_next;
delete cur;
prev->_next = next;
next->_prev = prev;
--_size;
}
size_t size()
{
return _size;
}
void clear()
{
iterator it = begin();
while (it != end)
{
it = erase(it);
}
}
void push_back(const T& x)
{
insert(end(), x);
}
void push_front(const T& x)
{
insert(begin(), x);
}
void push_back()
{
erase(end());
}
void pop_back()
{
erase(begin());
}
private:
Node* _head;
size_t _size;
};
4、打印
template<typename Container>
void print_container(const Container& con)
{
typename Container::const_iterator it = con.begin();
while (it != con.end())
{
cout << *it << " ";
++it;
}
cout << endl;
}
void test_list()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
lt.push_back(5);
print_container(lt);
list<string> lt1;
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
print_container(lt1);
vector<string> v;
v.push_back("222222222222222222222");
v.push_back("222222222222222222222");
v.push_back("222222222222222222222");
v.push_back("222222222222222222222");
print_container(v);
}
}
int main()
{
bit::test_list();
return 0;
}
5、完整代码
#include<iostream>
#include<string>
#include<vector>
using namespace std;
namespace bit
{
template<class T>
struct list_node
{
T _data;
list_node<T>* _prev;
list_node<T>* _next;
list_node(const T& x = T())
:_data(x)
, _next(nullptr)
, _prev(nullptr)
{}
};
template<class T, class Ref, class Ptr>
struct __list_iterator
{
typedef list_node<T> Node;
typedef __list_iterator<T, Ref, Ptr> self;
Node* _node;
__list_iterator(Node* node)
:_node(node)
{}
self& operator++()
{
_node = _node->_next;
return *this;
}
self& operator--()
{
_node = _node->_prev;
return *this;
}
self operator++(int)
{
self tmp(*this);
_node = _node->_next;
return tmp;
}
self operator--(int)
{
self tmp(*this);
_node = _node->_prev;
return tmp;
}
Ref operator*()
{
return _node->_data;
}
Ptr operator->()
{
return &_node->_data;
}
bool operator!=(const self& s)
{
return _node != s._node;
}
bool operator==(const self& s)
{
return _node == s._node;
}
};
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 _head->_next;
}
iterator end()
{
return _head;
}
const_iterator begin() const
{
return _head->_next;
}
const_iterator end() const
{
return _head;
}
void empty_init()
{
_head = new Node;
_head->_next = _head;
_head->_prev = _head;
_size = 0;
}
list()
{
empty_init();
}
list(list<T>& lt)
{
empty_init();
for (auto e : lt)
{
push_back(e);
}
}
list<T>& operator=(list<T> lt)
{
swap(lt);
return *this;
}
void swap(list<T> lt)
{
std::swap(_size, lt._size);
std::swap(_head, lt._head);
}
iterator insert(iterator pos, const T& x)
{
Node* cur = pos._node;
Node* newnode = new Node(x);
Node* prev = cur->_prev;
prev->_next = newnode;
newnode->_prev = prev;
newnode->_next = cur;
cur->_prev = newnode;
++_size;
return iterator(newnode);
}
iterator erase(iterator pos)
{
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* next = cur->_next;
delete cur;
prev->_next = next;
next->_prev = prev;
--_size;
}
size_t size()
{
return _size;
}
void clear()
{
iterator it = begin();
while (it != end)
{
it = erase(it);
}
}
void push_back(const T& x)
{
insert(end(), x);
}
void push_front(const T& x)
{
insert(begin(), x);
}
void push_back()
{
erase(end());
}
void pop_back()
{
erase(begin());
}
private:
Node* _head;
size_t _size;
};
template<typename Container>
void print_container(const Container& con)
{
typename Container::const_iterator it = con.begin();
while (it != con.end())
{
cout << *it << " ";
++it;
}
cout << endl;
}
void test_list()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
lt.push_back(5);
print_container(lt);
list<string> lt1;
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
lt1.push_back("1111111111111");
print_container(lt1);
vector<string> v;
v.push_back("222222222222222222222");
v.push_back("222222222222222222222");
v.push_back("222222222222222222222");
v.push_back("222222222222222222222");
print_container(v);
}
}
int main()
{
bit::test_list();
return 0;
}
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