#include <iostream>
#include <stdexcept>
#include <utility>
#include <vector>

class Jump_List
{
private:

    struct Node;
    
public:

    Jump_List() = default;
    
    int& at(int index)
    {
        Node* current { first };

        if (index >= count)
        {
            throw std::out_of_range { "Jump_List out of range" };
        }
        
        if (index % 2 == 1)
        {
            current = current->next;
            --index;
        }

        while (index > 0)
        {
            current = current->jump;
            index -= 2;
        }

        return current->value;
    }

    void pop_front()
    {
        Node* tmp { first };
        first = first->next;
        delete tmp;
        --count;
    }

    int size() const
    {
        return count;
    }

    void print(std::ostream& os) const
    {
        Node* current { first };
        os << "size " << size() << ": ";
        while (current != nullptr)
        {
            os << current->value << " ";
            current = current->next;
        }
        os << std::endl;
    }
    
private:

    struct Node
    {
        int value { };
        Node* jump { };
        Node* next { };
    };

    Node* first { };
    int count { };
};

int main()
{
    Jump_List l1 { };
    for (int i { 9 }; i >= 0; --i)
    {
        l1.push_front(i);
    }

    Jump_List l2 { l1 };
    
    for (int i { 0 }; i < 4; ++i)
    {
        l1.pop_front();
    }

    l1.print(std::cout);
    l2.print(std::cout);

    // TODO: Insert tests for move and copy-semantics.
}