class List
{
public:
    struct Node
    {
        Node(const int& data, Node* next=0):data(data),next(next) {}
        Node* next;
        int data;
    };

    List() : head(0) {}

    List(const List& L) : head(0)
    {
        for ( const Node* i = L.begin(); i!= L.end(); i=i->next )
            push_front(i->data);
        reverse();
    }

    void reverse()
    {
        Node* p = 0; Node* i = begin(); Node* n;
        while (i)
        {
            n = i->next;
            i->next = p;
            p = i; i = n;
        }
        head = p;
    }

    void swap(List& x)
    {
        Node* tmp = head; head = x.head; x.head = tmp;
    }

    List& operator=(const List& x)
    {
        List tmp(x);
        swap(tmp);
        return *this;
    }

    ~List() { clear(); }
    void clear() { while (!empty()) pop_front(); }

    bool empty() { return ! head; }

    void push_front(const int& x) {
        Node* tmp = new Node(x,head); head = tmp;
    }

    void pop_front() {
        if (head) { Node* tmp = head; head=head->next; delete tmp; }
    }

    void insert_after(Node* x, const int& data)
    {
        Node* tmp = new Node(data, x->next);
        x->next = tmp;
    }

    void erase_after(Node* x)
    {
        Node* tmp = x->next;
        if (tmp)
        {
            x->next = x->next->next;
            delete tmp;
        }
    }


    int& front() { return head->data; }
    const int& front() const { return head->data; }

    Node* begin() { return head; }
    Node* end() { return 0; }

    const Node* begin() const { return head; }
    const Node* end() const { return 0; }

private:
    Node* head;
};

#include <iostream>
using namespace std;

int main()
{
    List X;
    X.push_front(3);
    X.push_front(2);
    X.push_front(1);

    for (List::Node* it = X.begin(); it; it = it->next )
        cout << it->data << endl;

    X.reverse();

    for (List::Node* it = X.begin(); it; it = it->next )
        cout << it->data << endl;
    return 0;
}