$1.$ Write a class List for a doubly$-$linked list of characters, using a circular linked list

with a dummy node $($List$.$h$,$ List.cc$).$ The nodes $($Element$)$ should be declared as

a private nested class. Also declare iterator as a public nested class. For simplicity,

you do not need to implement const$\_$iterator.

You should implement the following member functions:

$$ Default constructor: initializes the list to an empty list.

$$ Destructor: deletes all nodes in the list.

$$ begin$(),$ end$()$: return iterators that point to the beginning and $$one$-$past$-$theend$$

of the list. Note that if the list is empty, then begin$()==$ end$().$

$$ void insert$($iterator it$,$ char c$)$: inserts the character c into the position

specified by the iterator it$.$ If it $==$ end$(),$ the character is appended to the

list.

$$ void erase$($iterator it$)$: erases the character at the position specified by the

iterator it$.$ If it $==$ end$(),$ this function does nothing.

Make sure that List is a friend of iterator. For the iterator nested class, implement

the following member functions:

$$ A default constructor which initializes the pointer to nullptr.

$$ A private constructor which takes a pointer to Element and initializes itself to the

pointer. Making the constructor private means that only List member functions

can initialize an iterator directly.

$$ The pre$-$increment operator $(++)$ which moves to the next element. You can

assume that the iterator is not one$-$past$-$the$-$end of the list.

$$ The pre$-$decrement operator $(--)$ which moves to the previous element. You can

assume that the iterator is not at the beginning of the list.

$$ The dereference operator $(*).$ Provide two versions of the dereference operator:

one returning a reference to the character data, and another returning a constant

reference.

$$ The comparison operators $==$ and $!=$ which compare the pointers.

Modify the posted solution of Assignment $4$ Question $1$ to use the List class instead

of the STL list class. Put this in prob$1.$cc$.$