If you have a function which returns true if a node is a descendant of another node as in

        boolean is_descendant (NODE a, NODE b); // returns true if node b is a descendant of node a

then do not allow the insertion of a child to a node if that node is a descendant of the child.

Dave Diaz


> -----Original Message-----
> From: Tracy Pierce [SMTP:[log in to unmask]]
> Sent: 26 December 2001 19:04
> To:   [log in to unmask]
> Subject:      [HP3000-L] TREES: anti-loop algorithm?
>
> I have a set of activities which sometimes include other activities; this is
> recursive, the result resembles a tree structure, similar to a directory
> tree.  Until now I've quite simply disallowed 'multiple parents', but
> largely because my brain's too feeble to see a cleaner loop-avoidance
> mechanism.
>
> (Clear as mud?  Here I have A includes B & D, B includes C, E includes F,
> all just lovely.  This works nicely even in a physical sense, and looks like
> a tree.)
>
> ActA
>  |-ActB
>  |-ActC
>     |-ActD
> ActE
>  |-ActF
>
> Now I need to add ActF to ActC, basically meaning I want to allow leaf F
> appear on multiple trees.  This is ok, but the procedure of adding ActF to
> ActC must include enough exhaustive checking to ensure that I disallow
> creation of loops, such as that which would occur if I were to add ActA to
> ActC.
>
> Can anyone here on good old HP3000-L point me in the direction of the
> perfect solution?  (I just KNOW there are papers out there, so even a good
> Google key would be a great pointer!)
>
> TIA
>
> Tracy Pierce
>
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