Question

Please only edit the list.cpp file only, implement the push_front method that will insert a new element to the front of the list.

//list.h // Doubly linked list #ifndef Q2_H #define Q2_H template<typename T> class List; template<typename T> class Iterator; template <typename T> class Node {    public:        Node(T element);    private:        T data;        Node* previous;        Node* next;    friend class List<T>;    friend class Iterator<T>; }; template <typename T> class List {    public:        List(); // Constructor        ~List(); // Destructor        void push_front(T element); // Inserts to front of list        Iterator<T> begin(); // Point to beginning of list        Iterator<T> end(); // Point to past end of list    private:        Node<T>* head;        Node<T>* tail;    friend class Iterator<T>; }; template <typename T> class Iterator {    public:        Iterator();        T get() const; // Get value pointed to by iterator        void next(); // Advance iterator forward        void previous(); // Advance iterator backward        bool equals(Iterator<T> other) const; // Compare values pointed to by two iterators    private:        Node<T>* position; // Node pointed to by iterator        List<T>* container; // List the iterator is used to iterate    friend class List<T>; }; #endif

//list.cpp // Implement the push_front method #include <string> #include "q2.h" using namespace std; // Node class implemenation template <typename T> Node<T>::Node(T element) { // Constructor    data = element;    previous = nullptr;    next = nullptr; } // List implementation template <typename T> List<T>::List() {    head = nullptr;    tail = nullptr; } template <typename T> List<T>::~List() { // Destructor    for(Node<T>* n = head; n != nullptr; n = n->next) {           delete n; //Deconstructor create an error evertime i ran it.    } } template <typename T> void List<T>::push_front(T element) {    // Your code here } template <typename T> Iterator<T> List<T>::begin() {    Iterator<T> iter;    iter.position = head;    iter.container = this;    return iter; } template <typename T> Iterator<T> List<T>::end() {    Iterator<T> iter;    iter.position = nullptr;    iter.container = this;    return iter; } // Iterator implementation template <typename T> Iterator<T>::Iterator() {    position = nullptr;    container = nullptr; } template <typename T> T Iterator<T>::get() const {    return position->data; } template <typename T> void Iterator<T>::next() {    position = position->next; } template <typename T> void Iterator<T>::previous() {    if (position == nullptr) {        position = container->tail;    } else {        position = position->previous;    } } template <typename T> bool Iterator<T>::equals(Iterator<T> other) const { return position == other.position; }

list_test.cpp // Test for push_front method #include <iostream> #include "q2.h" #include "q2.cpp" using namespace std; int main() {    List<string> stack;    stack.push_front("My");    stack.push_front("name");    stack.push_front("is");    stack.push_front("Ozymandias");    stack.push_front("king");    stack.push_front("of");    stack.push_front("kings");    // Should print - kings of king Ozymandias is name My    for (auto p = stack.begin(); !p.equals(stack.end()); p.next())        cout << p.get() << " ";    cout << endl; }

Answer 1

The required code followed by the screenshot of output has been added below, please note that the modification is in list.cpp file only so I have given only that file not all. Also to run your code, replace q2 with list in remaining files as q2 do not exist here to include. The explanation of the modified code has been added in front of it in comment lines.

CODE:

//list.cpp

// Implement the push_front method

#include <string>
#include "list.h"

using namespace std;

// Node class implemenation

template <typename T>
Node<T>::Node(T element) { // Constructor
   data = element;
   previous = nullptr;
   next = nullptr;
}

// List implementation

template <typename T>
List<T>::List() {
   head = nullptr;
   tail = nullptr;
}


template <typename T>
List<T>::~List() { // Destructor
   for(Node<T>* n = head; n != nullptr; n = n->next) {

       delete n; //Deconstructor create an error evertime i ran it.
   }

}

template <typename T>
void List<T>::push_front(T element) {
    Node<T>* newnode = new Node<T>(element);    // made a new node

    Iterator<T> iterhead;                       // made an iterator for head
    iterhead.position = head;                   // set its position to head

    Iterator<T> iternew;                        // made an iterator for new
    iternew.position = newnode;                 // set its position to new

    iternew.position->next = head;              // set the next of new node to head
    if (head == nullptr)                        // if head is null then add the newnode to tail
        tail = newnode;
    else                                        // else add to the previous of head
        iterhead.position->previous = newnode;

    head = newnode;                             // in last made the new node to head.
}


template <typename T>
Iterator<T> List<T>::begin() {
   Iterator<T> iter;
   iter.position = head;
   iter.container = this;
   return iter;
}

template <typename T>
Iterator<T> List<T>::end() {
   Iterator<T> iter;
   iter.position = nullptr;
   iter.container = this;
   return iter;
}

// Iterator implementation

template <typename T>
Iterator<T>::Iterator() {
   position = nullptr;
   container = nullptr;
}


template <typename T>
T Iterator<T>::get() const {
   return position->data;
}

template <typename T>
void Iterator<T>::next() {
   position = position->next;
}

template <typename T>
void Iterator<T>::previous() {
   if (position == nullptr) {
       position = container->tail;
   } else {
       position = position->previous;
   }
}

template <typename T>
bool Iterator<T>::equals(Iterator<T> other) const {
return position == other.position;
}

OUTPUT:

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