On Tue, 2010-06-01 at 11:42 -0700, Peter Zijlstra wrote:
> On Tue, 2010-06-01 at 11:09 -0700, Venkatesh Pallipadi wrote:
> > On Tue, Jun 1, 2010 at 10:42 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > On Tue, 2010-06-01 at 10:34 -0700, Venkatesh Pallipadi wrote:
> > >>
> > >> Yes. This will cover all the cases on insert. But on erase, there is
> > >> still a case where a rotate of sibling node is done during the
> > >> re-coloration process. There we have a child change on sibling's
> > >> child. I am not able to think of any easy way to handle that case.
> > >
> > > Let me go draw some figures with pen and paper to match up the erase
> > > path with the rb_augment_erase_begin() code, because I can't quite spot
> > > the case we're missing.
> > >
> > > If you have it handy, ascii art might help..
> >
> > It is this case
> >
> > P
> > / \
> > N S
> > / \
> > SL SR
> >
> > changing to
> >
> > P
> > / \
> > N SL
> > \
> > S
> > \
> > SR
>
> Right, but see: http://en.wikipedia.org/wiki/Red-black_tree
> That is delete_case5, however then we fall into delete_case6 and perform
> a left rotation.
>
> So suppose we start with the tree:
>
> P P P SL
> / \ / \ / \ / \
> D S --> N S --> N SL --> P S
> \ / \ / \ \ / \
> N SL SR SL* SR S* N SR
> \
> SR
>
> and then remove D, delete case 5 and finally delete case 6, * marks red.
>
> rb_augment_erase_begin(D) will return N, and then rb_augment_path(N)
> will re-augment: N, P, SL and S.
P SL
/ \ / \
N S ---> N S
/ / \ / \
C SL SR C SR
If P needs to be removed, we need to re-augment S also in this case,
right? It looks like we are not handling this case.
thanks,
suresh
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