Question 3. Enqueue and dequeue using a linked list [6]

Given the definitions below for a linked list class and a queue class, provide appropriate implementations for the enqueue and dequeue methods. 
class List {
   private: // internal list and node composition
      struct Lnode {
         string data;
         Lnode *next, *prev;
      };
      Lnode *front, *back;
   public:
      List(); // empty list constructor
     ~List(); // deallocate remaning nodes
      // routines to insert a new node at the front or back
      //    of the list, returning true iff successful
      bool insertAtFront(string s);
      bool insertAtBack(string s);
      // routines to copy front or back string out of the list
      //    and delete the node, returing true iff successful
      bool removeFromFront(string &s);
      bool removeFromBack(string &s);
};

class Queue {
   private: 
      // internally the queue is stored as a list
      List Q;
   public:
      Queue(); // empty queue constructor
     ~Queue(); // deallocate remaining queued items

      // add new item to back of queue,
      //    returning true iff successful
      bool enqueue(string s);

      // remove front item from queue (copy into s)
      //    returning true iff successful
      bool dequeue(string &s);
};

SAMPLE SOLUTION

bool Queue::enqueue(string s)
{
   return Q.insertAtBack(s);
}

bool Queue::dequeue(string &s)
{
   return Q.removeFromFront(s);
}