How to implement a double linked list with only one pointer?

Question

How to implement a double linked list with only one pointer?

It takes O(1) time to find the prev and next Node.

struct Node
{
   int val;
   Node* p;
};

Answer 1

There is a classic hack: store the XOR of the 2 pointers (Prev and Next) and when traveling the list you always have 1 of those at hand (you just came from there) and you can XOR it with the stored value to get the other pointer.

Needless to say that this won't work in a GC environment.