Re: [xsl] Sudoku stylesheet

[andrew welch <andrew.j.welch@xxxxxxxxx>]

On 2/13/06, Michael Kay <mike@xxxxxxxxxxxx> wrote:
> > The reason why this is so hard with XSLT is because you can't update
> > variables, which rules out Backtracking.
>
> No: my knight's tour stylesheet does backtracking quite happily. The two
> problems seem conceptually quite similar. The main difficulty in both cases
> is that each "move" involves a small change to a fairly large data
> structure, which can be quite inefficient since it's likely that the entire
> structure will be copied. For this reason in the knight's tour the most
> efficient solution was the one that represented the entire board as a
single
> string value, and I suspect this might also be the most efficient
> representation of a SuDoKu board.
>
> You need to have enough stack available to handle the maximum number of
> moves recursively, but at 81 that shouldn't be too difficult.

Yes I thought of your Knights Tour stylesheet as I wrote that - the
crucial difference for me is that Backtracking involves unwinding the
stack and carrying on with a different value, whereas in XSLT you
can't unwind the stack - there is no *back* tracking as such - you
just carry on from the same point (which is why you need all that
stack).

I think I have my pedant hat on, with lots of split hairs hanging out
the back....