1. 什么是list

list是一个顺序表，底层采用双向带头循环链表实现，支持常量时间的插入删除操作，不同于vector无法随机访问。

2. 模拟实现

反向迭代器可作为适配器，是正向迭代器的封装：

cpp 复制代码

#pragma once
namespace lzh {
	template<class Iterator, class Ref, class Ptr>
	struct ReverseIterator {
		typedef ReverseIterator<Iterator, Ref, Ptr> self;
		ReverseIterator(Iterator it) :_it(it) { }

		self& operator++() {
			--_it;
			return *this;
		}

		self& operator--() {
			++_it;
			return *this;
		}

		Ref& operator*() {
			Iterator temp = _it;
			return *--temp;
		}

		Ptr operator->() {
			return &(operator*());
			//return _it.operator->();
		}

		bool operator!=(const self& it) {
			return _it != it._it;
		}

		Iterator _it;
	};
}

list模拟实现：

cpp 复制代码

#pragma once
#include <iostream>
#include <algorithm>
#include <algorithm>
#include <utility>
#include <assert.h>

using namespace std;
namespace lzh {
	template<class T>
	struct list_node { 
		list_node(const T& val = T()) :_val(val), _next(nullptr), _prev(nullptr)
		{ }

		T _val;
		list_node<T>* _next;
		list_node<T>* _prev;
	};

	template<class T, class Ref, class Ptr>
	struct list_iterator {
		typedef list_node<T> list_node;
		typedef list_iterator<T, T&, T*>             iterator;
		typedef list_iterator<T, const T&, const T*> const_iterator;
		typedef list_iterator<T, Ref, Ptr>			 self;

		list_iterator(list_node* ptr) :_ptr(ptr)
		{ }

		list_iterator(const iterator& it) :_ptr(it._ptr)
		{ }



		self& operator++() {
			_ptr = _ptr->_next;
			return *this;
		}

		self operator++(int) {
			self temp = *this;
			_ptr = _ptr->_next;
			return temp;
		}

		self& operator--() {
			_ptr = _ptr->_prev;
			return *this;
		}

		self operator--(int) {
			self temp = *this;
			_ptr = _ptr->_prev;
			return temp;
		}

		bool operator!=(const self& p) const {
			return _ptr != p._ptr;
		}

		Ref operator*() {
			return _ptr->_val;
		}

		Ptr operator->() {
			return &_ptr->_val;
		}
		list_node* _ptr;
	};

	template<class T>
	class list {
	private:
		typedef list_node<T> list_node;
		void empty_init() {
			_node = new list_node;
			_node->_next = _node->_prev = _node;
			_size = 0;
		}
	public:	  
		typedef list_iterator<T, T&, T*>			           iterator;
		typedef list_iterator<T, const T&, const T*>           const_iterator;

		typedef list_reverse_iterator<iterator, T&, T*>	              reverse_iterator;
		typedef list_reverse_iterator<const_iterator, const T&, const T*>   const_reverse_iterator;
		list() {
			empty_init();
		}
		list(size_t n, const T& val) {
			empty_init();
			for (size_t i = 0; i < n; ++i) {
				push_back(val);
			}
		}

		list(int n, const T& val) {
			empty_init();
			for (int i = 0; i < n; ++i) {
				push_back(val);
			}
		}
		// list(const list& lt)
		// 在类中可以直接写类名，但是不推荐
		// 为了可读性最好加上模板参数
		list(const list<T>& lt) {
			empty_init();
			for (auto& l : lt) {
				push_back(l);
			}
		}

		template <class Iterator>
		list(Iterator first, Iterator last) {
			empty_init();
			while (first != last) {
				push_back(*first);
				++first;
			}
		}

		void swap(list<T>& lt) {
			std::swap(_node, lt._node);
			std::swap(_size, lt._size);
		}

		list<T>& operator=(list<T> lt) {
			swap(lt);
			return *this;
		}

		~list() {
			clear();
			delete _node;
			_node = nullptr;
		}

		void clear() {
			iterator it = begin();
			while (it != end()) {
				it = erase(it);
			}
			_size = 0;
		}

		iterator begin() {
			// iterator(_node->_next)
			return _node->_next;
		}

		iterator end() {
			return _node;
		}

		const_iterator begin() const {
			return _node->_next;
		}

		const_iterator end() const {
			return _node;
		}

		reverse_iterator rbegin() {
			return end();
		}

		reverse_iterator rend() {
			return begin();
		}

		const_reverse_iterator rbegin() const {
			return end();
		}

		const_reverse_iterator rend() const {
			return begin();
		}

		void push_back(const T& val) {
			/*list_node* newNode = get_node(val);

			list_node* tail = _node->_prev;
			newNode->_next = _node;
			_node->_prev = newNode;

			newNode->_prev = tail;
			tail->_next = newNode;*/
			insert(end(), val);

		}
	
		void push_front(const T& val) {
			/*list_node* newNode = get_node(val);

			list_node* head = _node->_next;
			_node->_next = newNode;
			newNode->_prev = _node;

			newNode->_next = head;
			head->_prev = newNode;*/
			insert(begin(), val);
		}

		iterator insert(iterator pos, const T& val) {
			list_node* newNode = new list_node(val);
			list_node* prev = pos._ptr->_prev;
			newNode->_next = pos._ptr;
			pos._ptr->_prev = newNode;
			prev->_next = newNode;
			newNode->_prev = prev;

			++_size;
			return pos;
		}

		void pop_back() {
			/*assert(_node->_prev != _node);
			list_node* tail = _node->_prev;
			tail->_prev->_next = _node;
			_node->_prev = tail->_prev;
			delete tail;*/
			erase(--end());
		}

		void pop_front() {
			/*assert(_node->_next != _node);

			list_node* head = _node->_next;
			_node->_next = head->_next;
			head->_next->_prev = _node;
			delete head;*/
			erase(begin());
		}

		iterator erase(iterator pos) {
			//assert(pos._ptr != _node);
			assert(pos != end());
			list_node* prev = pos._ptr->_prev;
			list_node* next = pos._ptr->_next;
			prev->_next = next;
			next->_prev = prev;

			delete pos._ptr;
			--_size;
			return next;
		}

		// List Access
		T& front() {
			assert(!empty());
			return _node->_next->_val;
		}
		const T& front() const {
			assert(!empty());
			return _node->_next->_val;
		}		  

		T& back() {
			assert(!empty());
			return _node->_prev->_val;
		}
		const T& back() const {
			assert(!empty());
			return _node->_prev->_val;
		}

		bool empty() const {
			return _size == 0;
		}
		size_t size() const {
			return _size;
		}

	private:
		list_node* _node;
		size_t _size;
	};
}

【C++】list的模拟实现

目录

1. 什么是list

2. 模拟实现