Step by Step solution about How to resolve the algorithm Queue/Definition step by step in the C++ programming language

The provided C++ code defines a queue data structure using a singly linked list. Here's a detailed explanation of the code:

Class Definition:

namespace rosettacode
{
 template<typename T> class queue
 {
   // ...
 };
}

This code defines a class template queue that represents a queue data structure. It can store elements of any type T.

Node Structure:

template<typename T> struct queue<T>::node
{
 T data;
 node* next;
 node(T const& t): data(t), next(0) {}
};

This is a nested structure within the queue class. It represents individual nodes of the linked list that will store the elements of the queue. Each node contains a data field and a next field, which points to the next node in the list.

Constructor:

template<typename T>
queue<T>::queue():
 head(0)
{
}

The constructor initializes an empty queue. It sets the head pointer to 0, indicating that the queue is initially empty.

Destructor:

template<typename T>
queue<T>::~queue()
{
 while (!empty())
   drop();
}

The destructor properly deallocates the memory used by the queue. It calls the drop() method repeatedly until the queue is empty, which effectively deletes all the allocated nodes.

Drop Method:

template<typename T>
inline void queue<T>::drop()
{
 node* n = head;
 head = head->next;
 delete n;
}

The drop() method is used to remove the first node in the queue and advance the head pointer to the next node. It first stores the current head node in a temporary pointer n, then updates head to point to the next node, and finally deallocates the n node.

Push Method:

template<typename T>
void queue<T>::push(T const& t)
{
 node*& next = head? tail->next : head;
 next = new node(t);
 tail = next;
}

The push() method adds an element to the end of the queue. It first determines the next pointer, which is either the next pointer of the tail node (if the queue is not empty) or the head pointer (if the queue is empty).

It then allocates a new node with the specified element t and assigns it to the next pointer. After that, it updates the tail pointer to point to the newly added node.

Pop Method:

template<typename T>
T queue<T>::pop()
{
 T tmp = head->data;
 drop();
 return tmp;
}

The pop() method removes and returns the element at the front of the queue. It first stores the data from the head node in a temporary variable tmp. Then, it calls the drop() method to remove the head node and advance the head pointer. Finally, it returns the stored data tmp.

Empty Method:

template<typename T>
bool queue<T>::empty()
{
 return head == 0;
}

The empty() method checks if the queue is empty. It simply returns true if the head pointer is 0 (indicating an empty queue) and false otherwise.

namespace rosettacode
{
  template<typename T> class queue
  {
  public:
    queue();
    ~queue();
    void push(T const& t);
    T pop();
    bool empty();
  private:
    void drop();
    struct node;
    node* head;
    node* tail;
  };

  template<typename T> struct queue<T>::node
  {
    T data;
    node* next;
    node(T const& t): data(t), next(0) {}
  };

  template<typename T>
   queue<T>::queue():
    head(0)
  {
  }

  template<typename T>
   inline void queue<T>::drop()
  {
    node* n = head;
    head = head->next;
    delete n;
  }

  template<typename T>
   queue<T>::~queue()
  {
    while (!empty())
      drop();
  }

  template<typename T>
   void queue<T>::push(T const& t)
  {
    node*& next = head? tail->next : head;
    next = new node(t);
    tail = next;
  }

  template<typename T>
   T queue<T>::pop()
  {
    T tmp = head->data;
    drop();
    return tmp;
  }

  template<typename T>
   bool queue<T>::empty()
  {
    return head == 0;
  }
}