```Begin forwarded message:

> From: NILSSON Christer <christer.nilsson / nordicsolution.com>
> Date: December 30, 2005 4:09:59 AM CST
> To: James Edward Gray II <james / grayproductions.net>
> Subject: Re: Ruby Quiz Suggestion
> Reply-To: NILSSON Christer <christer.nilsson / nordicsolution.com>
>
> Hello James!

[snip]

> I found a short solution for Sudoku. It was originally written by
> Kevin Greer in JavaScript, but Ruby makes it look even nicer. I
> haven't seen the use of this data structure in Sudoku before.

[snip]

> regards
> Christer
>
> class Sudoku
>   def initialize s
>     @s=s
>   end
>
>   def solve a, b, c, d
>     return true if a==3
>     return solve(a+1, 0, c, d) if b==3
>     return solve(a, b+1, 0, d) if c==3
>     return solve(a, b, c+1, 0) if d==3
>     return solve(a, b, c, d+1) if @s[a][b][c][d]!=0
>
>     for digit in 1..9
>       if not occupied?(a, b, c, d, digit) then
>         @s[a][b][c][d] = digit
>         return true if solve(a, b, c, d+1)
>         @s[a][b][c][d] = 0
>       end
>     end
>     false
>   end
>
>   def occupied? a, b, c, d, digit
>     for x in 0..2
>       for y in 0..2
>         return true if @s[a][b][x][y]==digit # block
>         return true if @s[a][x][c][y]==digit # row
>         return true if @s[x][b][y][d]==digit # column
>       end
>     end
>     false
>   end
> end
>
> s = [[[[0,0,0],[0,7,1],[0,0,5]], [[5,0,0],[0,6,9],[0,7,1]],
> [[0,7,1],[8,5,3],[4,2,0]]],
>      [[[0,1,0],[0,0,2],[0,0,0]], [[7,8,0],[1,5,4],[0,9,2]],
> [[0,4,0],[3,6,0],[1,8,0]]],
>      [[[0,6,4],[0,2,3],[0,5,0]], [[9,0,5],[0,1,0],[0,0,0]],
> [[7,0,0],[5,9,0],[0,0,0]]]]
> sudoku = Sudoku.new(s)
> sudoku.solve(0,0,0,0)
>
>

```