To support this add the following functions to each of DList and Sentinel classes: These functions returns an iterator/const_iterator to the first node in the list, end() if list is empty. these functions returns an iterator/const_iterator to the node just after the last node in the linked list. Iterator/const_iterator classes The const_iterator and iterators must support the following operations: iterator advances to next node in list if iterator is not currently at end(). The iterator returned depends if it is prefix or postfix. prefix operator returns iterator to current node. postfix operator returns iterator to node before the increment. iterator refer to the node "previous" to the linked list. The iterator returned depends if it is prefix or postfix. prefix operator returns iterator to current node. postfix operator returns iterator to node before the decrement. returns a const reference to data in the node referred to by the iterator. returns a reference to data in the node referred to by the iterator. Please implement iterator and const_iterator for both the functions DList and Sentinel classes in C++ code language , thank you! .

1. To support this add the following functions to each of DList and Sentinel classes:
These functions returns an iterator/const_iterator to the first node in the list, end() if list is empty.
these functions returns an iterator/const_iterator to the node just after the last node in the linked
list.
Iterator/const_iterator classes
The const_iterator and iterators must support the following operations:
iterator advances to next node in list if iterator is not currently at end(). The iterator returned
depends if it is prefix or postfix. prefix operator returns iterator to current node. postfix operator
returns iterator to node before the increment.
iterator refer to the node "previous" to the linked list. The iterator returned depends if it is prefix
or postfix. prefix operator returns iterator to current node. postfix operator returns iterator to
node before the decrement.
returns a const reference to data in the node referred to by the iterator.
returns a reference to data in the node referred to by the iterator.
Please implement iterator and const_iterator for both the functions DList and Sentinel classes
in C++ code language , thank you!
#include
<iostream>
template <typename T>
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:

2. 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(){}

3. };
template <typename T>
void DList<T>::push_front(const T& data){
}
template <typename T>
DList<T>::~DList(){
}
template <typename T>
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--(){}

4. 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 <typename T>
void Sentinel<T>::push_front(const T& data){
}
template <typename T>
Sentinel<T>::~Sentinel(){
}