Swap_Elements_DoublyLinkedList

void Swap(element*& first, element*& el1, element*& el2, element*& last)
{
    bool f = false;
    bool l = false;
    if (el1 == first)
    {
        element* cur = new element;
        cur->prev = NULL;
        cur->next = first;
        first->prev = cur;
        first = cur;
        f = true;
    }

    if (el2 == last)
    {
        cur = new element;
        cur->next = NULL;
        cur->prev = last;
        last->next = cur;
        last = cur;
        l = true;
    }

    if (el1->next == el2 || el2->next == el1)
    {
        el1->prev->next = el2;
        el2->prev = el1->prev;

        el1->next = el2->next;
        el2->next->prev = el1;

        el2->next = el1;
        el1->prev = el2;
    }
    else
    {
        element* tmp1 = new element;
        tmp1->next = el1->next;
        tmp1->prev = el1->prev;

        element* tmp2 = new element;
        tmp2->next = el2->next;
        tmp2->prev = el2->prev;

        el1->prev->next = el2;
        el2->prev = el1->prev;

        el1->next = el2->next;
        el2->next->prev = el1;

        el1->prev = tmp2->prev;
        tmp2->prev->next = el1;

        el2->next = tmp1->next;
        tmp1->next->prev = el2;

        delete tmp1;
        delete tmp2;
    }

    if (f)
    {
        cur = first;
        first = first->next;
        first->prev = NULL;
        delete cur;
    }

    if (l)
    {
        cur = last;
        last = last->prev;
        last->next = NULL;
        delete cur;
    }
}