Linked Implementation of Queue ADT

Write this as a struct and a class in C++.

Sample struct to represent a queue node

struct node
{
    data-type value;
    node* next;
    
    node(data-type value, node* next = nullptr)
    {
        this->value = value;
        this->next = next;
    }
};

Class to represent a queue

Data members

• q_front - pointer to front (first) node in the list.
• q_back - pointer to back (last) node in the list.
• q_size - Number of items currently stored in queue.

Member Functions

1. Default constructor

   Sets queue to initial empty state. The queue front pointer and the queue back pointer should be set to nullptr. The queue size should be set to 0.

2. size()

   Returns the queue size.

3. empty()

   Returns true if the queue size is 0; otherwise, false.

4. clear()

   We can easily set the queue back to the empty state by repeatedly calling pop() until the queue is empty.

5. front()

   Returns the front item of the queue (q_front->value).

6. back()

   Returns the front item of the queue (q_back->value).

7. push()

   Inserts a new item at rear of queue.

   procedure push(value: item to insert)
       Allocate a new queue node, new_node
       
       new_node->value ← value
   
       if queue is empty
           q_front ← new_node
       else
           q_back->next = new_node
       end if
   
       q_back ← new_node
       q_size ← q_size + 1
   end procedure
   

8. pop()

   Removes the front item from queue.

   procedure pop()
       delete_node ← q_front
       q_front ← q_front->next
       
       if q_front == nullptr
           q_back ← nullptr
           
       Delete the node delete_node
       
       q_size ← q_size - 1
   end procedure
   

9. Copy Constructor

   procedure queue(x : reference to a constant queue)
       // Set the new queue object's list to empty
       q_front ← q_back ← nullptr
       q_size ← 0
       
       // Copy the other queue's linked list
       clone(x)
   end procedure
   

10. Copy Assignment Operator

    procedure operator=(x : reference to a constant queue)
        if this != &x
            // Make the left queue object empty
            clear()
        
            // Copy the other queue's linked list
            clone(x)
        end if
        
        return *this;
    end procedure
    

11. Destructor

    We can delete all of the dynamic storage for the stack by calling the clear() member function.

12. clone()

    Copies the linked list from the queue x to this object.

    procedure clone(x : reference to a constant queue)
        ptr ← x.q_front
        
        while ptr != nullptr
            push(ptr->value)
            ptr ← ptr->next
        end while
    end procedure