Below is the given code of implementation:

#include  #include  #include  #include  using namespace std; class List; class Iterator; class Node { public: /* Constructs a node with a given data value. @param s the data to store in this node */ Node(string s); /* Destructor */ ~Node() {} private: string data; Node* previous; Node* next; friend class List; friend class Iterator; }; class List { public: /** Constructs an empty list. */ List(); /* Destructor. Deletes Nodes that are dynamically allocated */ ~List(); /** Appends an element to the list. @param data the value to append */ void push_back(string data); /** Inserts an element into the list. @param iter the position before which to insert @param s the value to append */ void insert(Iterator iter, string s); /** Removes an element from the list. @param iter the position to remove @return an iterator pointing to the element after the erased element */ Iterator erase(Iterator iter); /** Gets the beginning position of the list. @return an iterator pointing to the beginning of the list */ Iterator begin(); /** Gets the past-the-end position of the list. @return an iterator pointing past the end of the list */ Iterator end(); bool empty(); private: Node* first; Node* last; friend class Iterator; }; class Iterator { public: /** Constructs an iterator that does not point into any list. */ Iterator(); /* Copy constructor */ Iterator(const Iterator & pos); /** Looks up the value at a position. @return the value of the node to which the iterator points */ string get() const; /** Advances the iterator to the next node. */ void next(); /** Moves the iterator to the previous node. */ void previous(); /** Compares two iterators. @param b the iterator to compare with this iterator @return true if this iterator and b are equal */ bool equals(Iterator b) const; /* Overloaded Operators */ bool operator==(const Iterator& b) const; bool operator!=(const Iterator& b) const; Iterator operator++(int unused); //postfix Iterator& operator++(); //prefix Iterator operator--(int unused); //postfix Iterator& operator--(); //prefix string operator*() const; private: Node* position; List* container; friend class List; }; Node::Node(string s) { data = s; previous = NULL; next = NULL; } List::List() { first = NULL; last = NULL; } List::~List() { if (!empty()) // if the list is nonempty { Node* node = this->first; while (node->next != NULL) { node = node->next; // jump to the next one delete node->previous; // deleting the memory for previous } if (node->next == NULL) // reaching the last node { delete node; } } } bool List::empty() { return (last == NULL); } void List::push_back(string data) { Node* new_node = new Node(data); if (last == NULL) // List is empty { first = new_node; last = new_node; } else { new_node->previous = last; last->next = new_node; last = new_node; } } void List::insert(Iterator iter, string s) { if (iter.position == NULL) { push_back(s); return; } Node* after = iter.position; Node* before = after->previous; Node* new_node = new Node(s); new_node->previous = before; new_node->next = after; after->previous = new_node; if (before == NULL) // Insert at beginning first = new_node; else before->next = new_node; } Iterator List::erase(Iterator iter) { assert(iter.position != NULL); Node* remove = iter.position; Node* before = remove->previous; Node* after = remove->next; if (remove == first) first = after; else before->next = after; if (remove == last) last = before; else after->previous = before; delete remove; Iterator r; r.position = after; r.container = this; return r; } Iterator List::begin() { Iterator iter; iter.position = first; iter.container = this; return iter; } Iterator List::end() { Iterator iter; iter.position = NULL; iter.container = this; return iter; } Iterator::Iterator() { position = NULL; container = NULL; } Iterator::Iterator(const Iterator & pos) { (*this) = pos; } string Iterator::get() const { assert(position != NULL); return position->data; } void Iterator::next() { assert(position != NULL); position = position->next; } void Iterator::previous() { assert(position != container->first); if (position == NULL) position = container->last; else position = position->previous; } bool Iterator::equals(Iterator b) const { return position == b.position; } bool Iterator::operator==(const Iterator& b) const { return position == b.position; } bool Iterator::operator!=(const Iterator& b) const { return position != b.position; } Iterator & Iterator::operator++() // prefix { assert(position != NULL); position = position->next; return *this; } Iterator Iterator::operator++(int unused) // postfix { assert(position != NULL); Iterator clone(*this); position = position->next; return clone; } Iterator & Iterator::operator--() //prefix { assert(position != container->first); if (position == NULL) position = container->last; else position = position->previous; return *this; } Iterator Iterator::operator--(int unused) { assert(position != container->first); Iterator clone(*this); if (position == NULL) position = container->last; else position = position->previous; return clone; } string Iterator::operator*() const { assert(position != NULL); return position->data; } 

Exercise P12.12. Turn the linked list implementation into a singly-linked list: Drop the previous pointer of the nodes and the previous member function of the iterator. Reimplement the other member functions so that they have the same effect as before. Hint: In order to remove an element in constant time, iterators should store the predecessor of the current node. (2) Based on Problem P12.12 Turn the linked List of strings implementation into a singly-linked list sList: Drop the previous pointer of the nodes and the previous member function of the iterator. Reimplement the other member functions so that they have the same effect as before. Hint: In order to remove an element in constant time, iterators should store the predecessor of the current node. You can modify the List class provided in class (see the implementation posted on CCLccle) Write a program that reads the data from data2.txt into the single-linked list sList. Display the elements of the list and then prompt the user to enter an element for removal Implement a loop in which the removal action is performed until the user requests to quit Submit the solution as hmw.6.2.cpp Sample input-output - 23 data2.txt Notepad Iterating through the list in data2.txt: ello-World-Again-onorrow-Iowa esting Removal Enter the elenent to renove: Hello pdated list: World->Again-Tonorrow->Iowa :ontinue (y)? y Enter the element to renove: World pdated list Again->Tonorrow->Iowa ontinue (y>? y Enter the element to renove: Monday There is no such element in the list. ontinue y> y Enter the element to renove Iowa pdated list: Again->onorow File Edit Format View Hel 1 0 world Again Tomorr ow Iowa Press any key to continue . - . Ln 1, Col 1 Exercise P12.12. Turn the linked list implementation into a singly-linked list: Drop the previous pointer of the nodes and the previous member function of the iterator. Reimplement the other member functions so that they have the same effect as before. Hint: In order to remove an element in constant time, iterators should store the predecessor of the current node. (2) Based on Problem P12.12 Turn the linked List of strings implementation into a singly-linked list sList: Drop the previous pointer of the nodes and the previous member function of the iterator. Reimplement the other member functions so that they have the same effect as before. Hint: In order to remove an element in constant time, iterators should store the predecessor of the current node. You can modify the List class provided in class (see the implementation posted on CCLccle) Write a program that reads the data from data2.txt into the single-linked list sList. Display the elements of the list and then prompt the user to enter an element for removal Implement a loop in which the removal action is performed until the user requests to quit Submit the solution as hmw.6.2.cpp Sample input-output - 23 data2.txt Notepad Iterating through the list in data2.txt: ello-World-Again-onorrow-Iowa esting Removal Enter the elenent to renove: Hello pdated list: World->Again-Tonorrow->Iowa :ontinue (y)? y Enter the element to renove: World pdated list Again->Tonorrow->Iowa ontinue (y>? y Enter the element to renove: Monday There is no such element in the list. ontinue y> y Enter the element to renove Iowa pdated list: Again->onorow File Edit Format View Hel 1 0 world Again Tomorr ow Iowa Press any key to continue . - . Ln 1, Col 1