> For example, "How do you find the middle element of a singly linked list in one pass?" The answer, without comment, makes a presumption about how to define the "middle" of a list with even length. And it defines a linked list implementation with a magic, invisible head that requires extra code beyond the loop to compensate for.

I'm not sure what you mean by complaining about a magic, invisible head to the linked list. If you can't access the head of a linked list, you can't access any other part of it either.

However, as another comment points out elsewhere in the thread, there is a bigger problem -- the solution offered uses more than one pass.