c++ abstract class with nested class. derived class and nested class

I have the task to write own containers Linked_list and Array_list. I have one interface for them:

typedef int value_type;
class Container 
{
public:
        class Iterator 
        {   
        public:
            Iterator();
            Iterator(value_type* other);
            Iterator(const Iterator& other);
            Iterator& operator=(const Iterator& other);
                    ...
        };

    Container();
    Container(const Container& other);
    ~Container();   

    virtual value_type& front() const=0;
    virtual value_type& back() const=0;
    virtual Iterator begin() const=0; // 
    ...
};

I did derived classes Linked_list and Array_list:

class Linked_list:public Container 
{
public:
    long int cur_size;
    List elem;
    static Link end_;
    class Iterator: public Container::Iterator
    {
        friend Linked_list;
        Link *p;    
    };

    Iterator begin() const; //overriding virtual function return type differs ...

...
}

I thinks it's all wrong. should nested class Linked_list::Iterator be a derived class? Is it possible to do this, if I can't change the interface?