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SubjectRe: [PATCH 00/13] rbtree updates
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On Wed, 2012-07-11 at 18:12 -0700, Michel Lespinasse wrote:
>
> In __rb_erase_color(), some of the cases are more complicated than you drew however, because some node colors aren't known.

Right, the wikipedia article draws them blank, I couldn't come up with a
3rd case, although maybe we can annotate them like (P) to mean blank..


> This is what I ended up with:
>
> * 5), then the longest possible path due to 4 is 2B.
> *
> * We shall indicate color with case, where black nodes are uppercase and red
> - * nodes will be lowercase.
> + * nodes will be lowercase. Unknown color nodes shall be drawn as red with
> + * some accompanying text comment.
> */
>
> + /*
> + * Case 2 - sibling color flip
> + * (p could be either color here)
> + *
> + * p p
> + * / \ / \
> + * N S --> N s
> + * / \ / \
> + * Sl Sr Sl Sr
> + *
> + * This leaves us violating 5), so
> + * recurse at p. If p is red, the
> + * recursion will just flip it to black
> + * and exit. If coming from Case 1,
> + * p is known to be red.
> + */
>
> + /*
> + * Case 3 - right rotate at sibling
> + * (p could be either color here)
> + *
> + * p p
> + * / \ / \
> + * N S --> N Sl
> + * / \ \
> + * sl Sr s
> + * \
> + * Sr
> + */
>
> + /*
> + * Case 4 - left rotate at parent + color flips
> + * (p and sl could be either color here.
> + * After rotation, p becomes black, s acquires
> + * p's color, and sl keeps its color)
> + *
> + * p s
> + * / \ / \
> + * N S --> P Sr
> + * / \ / \
> + * sl sr N sl
> + */


Yes, very nice.. someday when I'm bored I might expand the comments with
the reason why we're doing the given operation.

Also, I was sorely tempted to rename your tmp1,tmp2 variables to sl and
sr.


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