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☀️走在路上，不忘来时的初心

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一、 list的介绍

1. 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。
2. 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。
3. 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。
4. 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。
5. 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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