C++ Implementation Double-Ended Queue

// C++ Program to Implement Double Ended Queue #include <iostream> #include <stdexcept> using namespace std; // Template class for a doubly linked list based Deque template <typename T> class Deque { private:  // Node structure representing each element in the Deque  struct Node {  // Data held by the node  T data;  // Pointer to the previous node  Node* prev;  // Pointer to the next node  Node* next;  // Constructor to initialize a Node with a given  // value  Node(T value)  : data(value)  , prev(nullptr)  , next(nullptr)  {  }  };  // Pointer to the front of the Deque  Node* front;  // Pointer to the rear of the Deque  Node* rear;  // Number of elements in the Deque  int size; public:  // Constructor to initialize an empty Deque  Deque()  : front(nullptr)  , rear(nullptr)  , size(0)  {  }  // Destructor to clean up memory by removing all  // elements  ~Deque()  {  while (!is_empty()) {  pop_front();  }  }  // Function to add an element to the front of the Deque  void push_front(T value)  {  // Create a new node  Node* new_node = new Node(value);  // If Deque is empty, both front and rear point to  // the new node  if (is_empty()) {  front = rear = new_node;  }  else {  // Link the new node to the current front  new_node->next = front;  // Link the current front to the new node  front->prev = new_node;  // Update front to the new node  front = new_node;  }  // Increment the size of the Deque  size++;  }  // Function to add an element to the back of the Deque  void push_back(T value)  {  Node* new_node  = new Node(value); // Create a new node  if (is_empty()) {  // If Deque is empty, both front and rear point  // to the new node  front = rear = new_node;  }  else {  // Link the new node to the current rear  new_node->prev = rear;  // Link the current rear to the new node  rear->next = new_node;  // Update rear to the new node  rear = new_node;  }  // Increment the size of the Deque  size++;  }  // Function to remove an element from the front of the  // Deque  void pop_front()  {  if (is_empty()) {  // Throw an error if Deque is empty  throw runtime_error("Deque is empty");  }  // Temporarily hold the front node  Node* temp = front;  // Move front to the next node  front = front->next;  if (front == nullptr) {  // If Deque is now empty, set rear to null  rear = nullptr;  }  else {  // Otherwise, unlink the old front node  front->prev = nullptr;  }  // Free the memory of the old front node  delete temp;  // Decrement the size of the Deque  size--;  }  // Function to remove an element from the back of the  // Deque  void pop_back()  {  if (is_empty()) {  // Throw an error if Deque is empty  throw runtime_error("Deque is empty");  }  // Temporarily hold the rear node  Node* temp = rear;  // Move rear to the previous node  rear = rear->prev;  if (rear == nullptr) {  // If Deque is now empty, set front to null  front = nullptr;  }  else {  // Otherwise, unlink the old rear node  rear->next = nullptr;  }  // Free the memory of the old rear node  delete temp;  // Decrement the size of the Deque  size--;  }  // Function to get the element at the front of the Deque  T get_front()  {  if (is_empty()) {  // Throw an error if Deque is empty  throw runtime_error("Deque is empty");  }  // Return the data of the front node  return front->data;  }  // Function to get the element at the rear of the Deque  T get_rear()  {  if (is_empty()) {  // Throw an error if Deque is empty  throw runtime_error("Deque is empty");  }  // Return the data of the rear node  return rear->data;  }  // Function to check if the Deque is empty  bool is_empty()  {  // Deque is empty if size is 0  return size == 0;  }  // Function to get the number of elements in the Deque  int get_size()  {  // Return the current size of the Deque  return size;  }  // Function to display the elements of the Deque  void display()  {  // Start from the front node  Node* current = front;  while (current != nullptr) {  // Print the data of the current node  cout << current->data << " ";  // Move to the next node  current = current->next;  }  cout << endl;  } }; int main() {  // Create a Deque of integers  Deque<int> deque;  // Push elements to the front and back  deque.push_front(10);  deque.push_back(20);  deque.push_front(5);  deque.push_back(30);  // Display the Deque after pushes  cout << "Deque after pushes: ";  deque.display();  // Get and display the front and rear elements  cout << "Front element: " << deque.get_front() << endl;  cout << "Rear element: " << deque.get_rear() << endl;  // Pop elements from the front and back  deque.pop_front();  deque.pop_back();  // Display the Deque after pops  cout << "Deque after pops: ";  deque.display();  // Display the size of the Deque  cout << "Size of deque: " << deque.get_size() << endl;  return 0; }