#include <iostream>

struct node {
    int data;
    node *next;

    node(int d):
        data(d), next(NULL)
    {}
};

class List {
public:
    List():
        head(NULL), last(NULL), count(0)
    {}

    ~List()
    {
        clear();
    }

    void clear()
    {}

    node *push_back(int data)
    {
        node *temp = new node(data);
        
        if( empty() )
            head = temp;
        else
            last->next = temp;

        last = temp;
        count++;

        return temp;
    }

    node *push_front(int data)
    {
        node *temp = new node(data);

        if( empty() )
            last = temp;
        else
            temp->next = head;

        head = temp;
        count++;

        return temp;
    }

    inline bool empty()
    { return count==0; }

    inline node *begin()
    { return head; }

protected:
    node *head;
    node *last;
    int count;
};

int main()
{
    int i;

    List l;

    for( i=0 ; i<10 ; i++ )
        l.push_back(i);

    for( i=0 ; i<10 ; i++ )
        l.push_front(i);

    node *iter = l.begin();

    while( iter!=NULL )
    {
        std::cout << iter->data << ' ';
        iter = iter->next;
    }
    std::cout << std::endl;

    return 0;
}