Re: Help: my list adt is broken

[tmoran@acm.org]

Just approach the problem one step at a time.  An arbitrary node has
how many incoming and outgoing pointer fields?  You have two nodes to
move, so write down assignment statements to change all the pointers.
If a node is a head node, its prev is null, which means its actual
prev is "head".  So any assignment that uses x.prev.all needs an "if"
to check that x.prev is not null, and, if it is null, use "head"
instead.  Similarly for a tail node.  Now make sure that in the
assignment statements you haven't tried to use something's old value
after changing it, eg "x.next := something_new;" followed by using
x.next as if it still had something_old as its value.  If so, make a
temporary copy of something_old before destroying it with "x.next :=
something_new".