Re: sudoku in an sql statement

This needs to be published...

On Wed, Nov 4, 2009 at 4:18 PM, marcin mank <marcin(dot)mank(at)gmail(dot)com> wrote:
>> I think the Oracle guy's version could easily be adapted to PG 8.4 ---
>> those little rownum subqueries seem to be just a substitute for not
>> having generate_series(1,9), and everything else is just string-pushing.
>
> indeed.
>
> marcin=# with recursive x( s, ind ) as
> ( select sud, position( ' ' in sud )
>  from  (select '53  7    6  195    98    6 8   6   34  8 3  17   2
> 6 6    28    419  5    8  79'::text as sud) xx
>  union all
>  select substr( s, 1, ind - 1 ) || z || substr( s, ind + 1 )
>       , position(' ' in repeat('x',ind) || substr( s, ind + 1 ) )
>  from x
>     ,  (select gs::text as z from generate_series(1,9) gs)z
>  where ind > 0
>  and not exists ( select null
>                   from generate_series(1,9) lp
>                   where z.z = substr( s, ( (ind - 1 ) / 9 ) * 9 + lp, 1 )
>                   or    z.z = substr( s, mod( ind - 1, 9 ) - 8 + lp * 9, 1 )
>                   or    z.z = substr( s, mod( ( ( ind - 1 ) / 3 ), 3 ) * 3
>                                      + ( ( ind - 1 ) / 27 ) * 27 + lp
>                                      + ( ( lp - 1 ) / 3 ) * 6
>                                   , 1 )
>                 )
> )
> select s
> from x
> where ind = 0;
>                                         s
> -----------------------------------------------------------------------------------
>  534678912672195348198342567859761423426853791713924856961537284287419635345286179
> (1 row)
>
> Time: 472.027 ms
>
>
> btw: it is pretty cool to replace some of the numbers in input with
> spaces and see how the query finds multiple solutions
>
> btw2: is SQL with 'with recursive' turing-complete ? Anyone care to
> try a Brainf*ck interpreter ? :)
>
> Greetings
> marcin Mańk
>
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