# [R] [R-pkgs] sudoku

Martin Maechler maechler at stat.math.ethz.ch
Mon Jan 9 09:40:57 CET 2006

```First, "thanks a lot!" to David Brahms for finally tackling this
important problem, and keeping the R language "major league" !
;-) :-)  {but the "thanks!" is meant seriously!}

>>>>> "Detlef" == Detlef Steuer <detlef.steuer at hsu-hamburg.de>
>>>>>     on Sun, 8 Jan 2006 12:21:52 +0100 writes:

Detlef> Hey, you spoiled my course!  :-)

Detlef> I planned using this as an excersise.  Alternative
Detlef> ideas anyone ...

Well, you could *add* to it:

1) When I have been thinking about doing this myself (occasionally
in the past weeks), I had always thought that finding *ALL*
solutions was a very important property of the algorithm I would
want to design.
(since this is slightly more general and useful than proofing
uniqueness which the current algorithm does not yet do anyway).

2) The current sudoku() prints the result itself and returns a
matrix; improved, it should return an object of class "sudoku",
with a print() and a plot() method;
3) The plot() method should of course also work for unfinished
"sudoku" objects, and in fact, the *input* to sudoku() should
also be allowed to be a (typically unfinished) "sudoku" object.

4) Then you could have your students use "grid" and
grid.locator() for GUI *input* of a sudoku; i.e. you'd have
another function which returns a (typically unfinished)
"sudoku" object.

5) You could start looking at *solving* the more general sudokus
where the blocks are not 3x3 squares anymore, but more
general rectangular polygons of 9 squares each.

6) Now you need to refine the GUI from "4)" because your users
need to be able to *draw* the block shapes for the
generalized sudokus.

7) Given "1)" is solved, the problem of *generating* sudokus,
that David already mentioned in his announcement, becomes
more relevant: You want to be sure that the sudokus you
generate have exactly one solution.  And your generating
exactly 1 solution) and "erases" squares as much as possible,
always checking that no other solution becomes possible.

You see, there's lot of interesting exercises left for your
course. (;-)

Martin

Detlef> On Fri, 6 Jan 2006 11:43:44 -0500 "Brahm, David"
Detlef> <David.Brahm at geodecapital.com> wrote:

>> Any doubts about R's big-league status should be put to
>> rest, now that we have a Sudoku Puzzle Solver.  Take
>> that, SAS!  See package "sudoku" on CRAN.
>>
>> The package could really use a puzzle generator --
>> contributors are welcome!
>>
>> -- David Brahm (brahm at alum.mit.edu)

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