Solving a Sudoku using Recursive Subquery Factoring by Anton Scheffer

Author → Asif

Oracle Database 11g Release 2 introduces a new feature called Recursive Subquery Factoring. To solve this sudoku you first have to transforms this to a single string by appending all rows together For example (this is pretty genius):

with x( s, ind ) as



( select sud, instr( sud, ' ' )



from ( select '53  7    6  195    98    6 8   6   

34  8 3  17   2   6 6    28    419  5    8  79' sud from dual )



union all

select substr( s, 1, ind - 1 ) || z || substr( s, ind + 1 )

, instr( s, ' ', ind + 1 )

from x, ( select to_char( rownum ) z



from dual

connect by rownum <= 9

) z



where ind > 0

and not exists ( select null

from ( select rownum lp

from dual

connect by rownum <= 9)

where z = substr( s, trunc( ( ind - 1 ) / 9 ) * 9 + lp, 1 )

or    z = substr( s, mod( ind - 1, 9 ) - 8 + lp * 9, 1 )

or    z = substr( s, mod( trunc( ( ind - 1 ) / 3 ), 3 ) * 3

+ trunc( ( ind - 1 ) / 27 ) * 27 + lp

+ trunc( ( lp - 1 ) / 3 ) * 6, 1 )))



select s from x



where ind = 0

/

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