Node Copying

Make deep_copy() static and pass in a Node*
 Node*  Node::deep_copy(Node  *n)  {
     if  (n  ==  NULL)  return  NULL;
     Node  *r  =  new  Node(n->number);
     for  (Node  *c1  =  r,  *c2  =  n->next;  c2;
             c1  =  c1->next,  c2  =  c2->next)  {
         c1->next  =  new  Node(c2->number);
     }
     return  r;
 }