#include
	template
	class DList{
	struct Node{
	T data_;
	Node* next_;
	Node* prev_;
	Node(const T& data=T{},Node* next=nullptr, Node* prev=nullptr){
	data_=data;
	next_=next;
	prev_=prev;
	}
	};
	Node* front_;
	Node* back_;
	public:
	DList(){
	front_=nullptr;
	back_=nullptr;
	}
	void push_front(const T& data);
	~DList();
	class const_iterator{
	Node* curr_;
	const_iterator(Node* n){
	curr_=n;
	}
	public:
	const_iterator(){
	curr_=nullptr;
	}
	const_iterator& operator++(){}
	const_iterator operator++(int){}
	const_iterator& operator--(){}
	const_iterator operator--(int){}
	bool operator==(const_iterator rhs){}
	bool operator!=(const_iterator rhs){}
	const T& operator*()const{}
	};
	class iterator:public const_iterator{
	public:
	iterator();
	iterator& operator++(){}
	iterator operator++(int){}
	iterator& operator--(){}
	iterator operator--(int){}
	T& operator*(){}
	const T& operator*()const{}
	};
	const_iterator cbegin() const{ }
	iterator begin(){ }
	const_iterator cend() const{}
	iterator end(){}
	};
	template
	void DList::push_front(const T& data){
	**YOUR CODE**
	}
	template
	DList::~DList(){
	**YOUR CODE**
	}
	template
	class Sentinel{
	struct Node{
	T data_;
	Node* next_;
	Node* prev_;
	Node(const T& data=T{},Node* next=nullptr, Node* prev=nullptr){
	data_=data;
	next_=next;
	prev_=prev;
	}
	};
	Node* front_;
	Node* back_;
	public:
	Sentinel(){
	front_=new Node();
	back_=new Node();
	front_->next_=back_;
	back_->prev_=front_;
	}
	void push_front(const T& data);
	~Sentinel();
	class const_iterator{
	public:
	const_iterator(){}
	const_iterator& operator++(){}
	const_iterator operator++(int){}
	const_iterator& operator--(){}
	const_iterator operator--(int){}
	bool operator==(const_iterator rhs){}
	bool operator!=(const_iterator rhs){}
	const T& operator*()const{}
	};
	class iterator:public const_iterator{
	public:
	iterator();
	iterator& operator++(){}
	iterator operator++(int){}
	iterator& operator--(){}
	iterator operator--(int){}
	T& operator*(){}
	const T& operator*()const{}
	};
	const_iterator cbegin() const{}
	iterator begin(){}
	const_iterator cend() const{}
	iterator end(){}
	};
	template
	void Sentinel::push_front(const T& data){
	**YOUR CODE**
	}
	template
	Sentinel::~Sentinel(){
	**YOUR CODE**
	}

To support this add the following functions to each of DList and Sentinel classes:

iterator begin(); const_iterator cbegin() const;

These functions returns an iterator/const_iterator to the first node in the list, end() if list is empty.

iterator end(); const_iterator cend() const;

these functions returns an iterator/const_iterator to the node just after the last node in the linked list.

Please implement iterator and const_iterator for functions DList and Sentinel classes in C++ code language, thank you!