C++ 双向循环链表（无头节点）merge问题

Question

template<typename T>
void doubleCircularList<T>::merge(doubleCircularList<T> & a, doubleCircularList<T> & b)
{

if (!a.firstNode || !b.firstNode) 
{
    if (!a.firstNode && !b.firstNode)
        return;
    else if (a.firstNode) 
    {
        firstNode = a.firstNode;
        lastNode = a.lastNode;
    }
    else
    {
        firstNode = b.firstNode;
        lastNode = b.lastNode;
    }
}
else 
{    
    ListNode<T>*p = a.firstNode;
    ListNode<T>*q = b.firstNode;
    ListNode<T>*currentNode = nullptr;
    a.lastNode->next = b.lastNode->next = nullptr;
    while (p && q) 
    {
        if (p->element <= q->element)
        {
            if (currentNode) 
            {
                currentNode->next = p;
                currentNode->next->previous = currentNode;
                currentNode = currentNode->next;
                p = p->next;
            }
            else 
            {
                currentNode = firstNode = p;
                p = p->next;            
            }
        }
        if (p && p->element > q->element) 
        {
            if (currentNode)
            {
                currentNode->next = q;
                currentNode->next->previous = currentNode;
                currentNode = currentNode->next;
                q = q->next;
            }
            else
            {
                currentNode = firstNode = q;
                q = q->next;
            }        
        }
    }
    if (p)
    {
        currentNode->next = p;
        currentNode->next->previous = currentNode;
        lastNode = a.lastNode;
        firstNode->previous = lastNode;
        lastNode->next = firstNode;
    }
    if (q)
    {
        currentNode->next = q;
        currentNode->next->previous = currentNode;
        lastNode = b.lastNode;
        firstNode->previous = lastNode;
        lastNode->next = firstNode;
    }
}

ListSize = a.ListSize + b.ListSize;
a.firstNode = a.lastNode = b.firstNode = b.lastNode = nullptr;
a.ListSize = b.ListSize = 0;

}
哪个大佬，写一份不令尾节点置空的方法，我这个是令尾节点置空的方法，感觉不好

Answer 1

我自己写好了