template_class_"Queue".cpp

#include <iostream>
using namespace std;

template <typename T>
struct Node {
    T data;
    Node* next;
    Node* prev;
    Node(const T& value) : data(value), next(nullptr), prev(nullptr) {}
};

template <typename T>
class Queue {
private:
    Node<T>* head;
    Node<T>* tail;
    size_t count;

public:
    Queue() : head(nullptr), tail(nullptr), count(0) {}
    ~Queue() { clear(); }

    void enqueue(const T& value) {
        Node<T>* newNode = new Node<T>(value);
        if (empty()) {
            head = tail = newNode;
        }
        else {
            tail->next = newNode;
            newNode->prev = tail;
            tail = newNode;
        }
        ++count;
    }

    void dequeue() {
        if (empty()) {
            cout << "Queue is empty!" << endl;
            return;
        }
        Node<T>* temp = head;
        head = head->next;
        if (head) head->prev = nullptr;
        else tail = nullptr;
        delete temp;
        --count;
    }

    T front() const {
        if (empty()) {
            throw runtime_error("Queue is empty!");
        }
        return head->data;
    }

    bool empty() const { return count == 0; }
    size_t size() const { return count; }

    void clear() {
        while (!empty()) {
            dequeue();
        }
    }

    void print() const {
        Node<T>* temp = head;
        cout << "( ";
        while (temp) {
            cout << temp->data;
            if (temp->next) cout << ", ";
            temp = temp->next;
        }
        cout << " )" << endl;
    }
};

int main() {
    Queue<int> q;
    q.enqueue(1);
    q.enqueue(2);
    q.enqueue(3);

    cout << "Queue: ";
    q.print();

    cout << "Front: " << q.front() << endl;
    cout << "Size: " << q.size() << endl;

    q.dequeue();
    cout << "After dequeue: ";
    q.print();

    return 0;
}