类似于是双向循环带头链表，适合在任何位置进行插入，删除，与vector不同的一点是，不能中括号向数组一样访问，list的插入不会申请额外的空间，所以不会发生迭代器失效，但是删除的时候回删除空间，有可能会引起迭代器的失效
1.list的构造函数
无参构造拷贝构造迭代器构造n个val构造2.iterator的使用
begin、rbeginend、rend3.list的常用函数
empty：检查是否为空size：返回个数++、–、*、->的重载clear：清空容器insert插入、erase删除等模拟实现
#pragma once namespace ljc { template<class T> class ListNode//结点类 { public: T m_val; ListNode * m_prev; ListNode * m_next; ListNode(const T &val = T()) : m_prev(nullptr), m_next(nullptr), m_val(val) { } }; template<class T> class list//list类：双向循环带头链表 { ListNode<T> * m_head; void createHead() { m_head = new ListNode<T>; m_head->m_next = m_head->m_prev = m_head; } public: class iterator { public: ListNode<T> * m_pos; iterator(ListNode<T> * val = nullptr) : m_pos(val) { } T & operator*()const { return m_pos->m_val; } T * operator->()const { return &m_pos->m_val; } iterator operator++() { m_pos = m_pos->m_next; return *this; } iterator operator++(int) { iterator tmp = *this; m_pos = m_pos->m_next; return tmp; } iterator operator--() { m_pos = m_pos->m_prev; return *this; } iterator operator--(int) { iterator tmp = *this; m_pos = m_pos->m_prev; return tmp; } bool operator==(const iterator & ci) const { return m_pos == ci.m_pos; } bool operator!=(const iterator & ci) const { return m_pos != ci.m_pos; } }; list() { createHead(); } list(int n, const T &val = T()) { createHead(); int i; for (i = 0; i < n; i++) { push_back(val); } } list(iterator start, iterator finish) { createHead(); insert(end(), start, finish); } list(T * start, T * finish) { createHead(); insert(end(), start, finish); } list(list<T> & l) { createHead(); insert(end(), l.begin(), l.end()); } ~list() { erase(begin(), end()); delete m_head; } void clear() { erase(begin(), end()); } void push_back(const T &val) { insert(end(), val); } void push_front(const T &val) { insert(begin(), val); } void pop_front() { erase(begin()); } int empty() { if (!m_head) { return 1; } return 0; } int size() { ListNode<T> * cur = m_head; if (empty()) { return 0; } int tmp = 0; for (cur = m_head->m_next; cur != m_head; cur = cur->m_next) { tmp++; } return tmp; } iterator insert(iterator pos, const T &val) { ListNode<T> * cur = new ListNode<T>; ListNode<T> * npos = pos.m_pos; cur->m_val = val; cur->m_prev = npos->m_prev; cur->m_prev->m_next = cur; cur->m_next = npos; npos->m_prev = cur; return cur; } iterator insert(iterator pos, T * start, T * finish) { T * tmp; iterator tmpit = --pos; pos++; for (tmp = start; tmp != finish; tmp++) { insert(pos, *tmp); } return ++tmpit; } iterator insert(iterator pos, iterator start, iterator end) { iterator tmp; iterator tmpit = --pos; pos++; for (tmp = start; tmp != end; tmp++) { insert(pos, *tmp); } return ++tmpit; } iterator erase(iterator pos) { ListNode<T> * npos = pos.m_pos; ListNode<T> * res = npos->m_next; npos->m_next->m_prev = npos->m_prev; npos->m_prev->m_next = npos->m_next; delete npos; return res; } iterator erase(iterator start, iterator finish) { iterator i; for (i = start; i != finish; i++) { erase(i); } return finish; } iterator begin() { return m_head->m_next; } iterator end() { return m_head; } }; };