SUDOKU(6)                  OpenBSD Reference Manual                  SUDOKU(6)



NAME
       sudoku - sudoku board game

SYNOPSIS
       (play the game)
              sudoku [options] ...  [<filename>]

       (generate boards)
              sudoku -g [<num>] [options] ...

       (solve boards)
              sudoku -v [options] ...

       (calculate statistics)
              sudoku -s [options] ...

DESCRIPTION
       The sudoku board game is played on a 9x9 grid, divided into rows,
       columns, and 9 blocks of 3x3 squares. The objective is to fill the
       empty squares with the digits 1-9, so that each row, column, and block
       contains each of the digits 1-9 (and hence, it is not possible for any
       digit to appear twice in the same row, column or block).

EXAMPLE
       Consider the following board, and the squares marked `a'-`h' and `x':

         5 . a | 6 b 1 | . . .       The digits appearing in each of the
         7 9 . | . . . | c 6 8       squares `a'-`h' can be uniquely
         d 3 . | . 8 . | 7 . .       determined. For example, the value
        -------+-------+-------      at `a' must be 8, since an 8 appears
         . 5 . | 4 1 e | . . 2       in the other rows and columns of the
         . . 1 | f x . | 6 . .       block. Using similar logic, it must
         8 . . | . 3 7 | . 4 .       be true that:
        -------+-------+-------           b = 7        f = 8
         . . 4 | . 9 . | g 2 .            c = 1        g = 8
         2 8 h | . . . | . 9 7            d = 1        h = 5
         . . . | 5 i 8 | . . 6            e = 6        i = 2

       In contrast, it is not possible to uniquely determine the value of `x'
       with the given information - it could take either the value 2 or 5.
       The board now contains the squares:

         5 . 8 | 6 7 1 | . . .    It is now possible to determine the values
         7 9 . | . . . | 1 6 8    appearing in other empty squares.
         1 3 . | . 8 . | 7 . .
        -------+-------+-------
         . 5 . | 4 1 6 | . . 2
         . . 1 | 8 x . | 6 . .    <<< the value of x must now be 5.
         8 . . | . 3 7 | . 4 .
        -------+-------+-------
         . . 4 | . 9 . | 8 2 .
         2 8 5 | . . . | . 9 7
         . . . | 5 2 8 | . . 6

       Repeating this process a few more times reveals the solution:

         5 4 8 | 6 7 1 | 2 3 9
         7 9 2 | 3 4 5 | 1 6 8
         1 3 6 | 9 8 2 | 7 5 4
        -------+-------+-------
         3 5 7 | 4 1 6 | 9 8 2
         4 2 1 | 8 5 9 | 6 7 3
         8 6 9 | 2 3 7 | 5 4 1
        -------+-------+-------
         6 1 4 | 7 9 3 | 8 2 5
         2 8 5 | 1 6 4 | 3 9 7
         9 7 3 | 5 2 8 | 4 1 6

GAME INTERFACE
       The sudoku game has a simple text interface (using the curses(3)
       library). The board is displayed in the middle of the screen, along
       with a summary of the allowed key presses. The cursor can be moved
       around the board using the arrow keys or the standard vi(1) movement
       keys, and each square (except for the fixed board squares that are
       initially revealed) can be set to a given digit by pressing the
       corresponding number key, or cleared by pressing either the `0' or `.'
       keys.

   Generating a New Board
       A new board can be generated at any time by pressing the `n' key, and
       either a precanned or randomly generated board will be displayed.  If
       the -n command line option is set, then only precanned boards will be
       displayed.

   Entering a Custom Board
       A custom board (e.g. found on the internet, or published in a
       newspaper) can be entered into the game by first clearing the current
       board (press the `c' key), entering the published squares (using the
       cursor motion keys and entering the appropriate numbers), and then
       fixing the squares by pressing the `f' key. At this point, the entered
       squares will be fixed (and cannot be changed).

   Hints
       The interactive game provides a simple hint mechanism to provide
       assistance in solving the board. It attempts to highlight areas of the
       board where moves can be made. If repeated hints are requested, the
       system starts revealing the digit that can be placed on the board.

       Often the hints can be quite cryptic. For example, consider the board
       below:

           v v v

           . . 7 | . . 9 | . . .
           9 . 6 | 7 4 . | . 1 5
           . . 2 | 5 1 . | . . .
          -------+-------+-------
        >  6 . 5 | . 7 . | . . 8  <    The characters ><v^ highlight the
        >  . 7 . | . . . | . 3 .  <    area of the hint
        >  8 . . | . . . | 7 . 6  <
          -------+-------+-------
           . . . | . 6 7 | 8 . .
           7 4 . | . 5 . | 9 6 2
           . 6 . | 4 . . | . . .

           ^ ^ ^

       The system gives the hint `try the digit 3', but it is certainly not
       obvious, with the revealed squares, where the 3 goes.


OPTIONS
       -d     Describe the moves needed to solve the board. Can only be used
              with the -v option for solving precanned boards.

       -f<format>
              Set output format. The supported formats are:
                standard  Default text format; std is a shortcut.
                compact   Compact text format.
                csv       Comma separated values, suitable for importing
                          into a spreadsheet.
                postscriptps is a shortcut.
                html      Simple HTML.

       -g[<num>]
              Generate <num> boards (or just 1 board, if not specified) and
              write them to standard output.

       -n     No random boards generated in the interactive game. Requires the
              optional file of precanned boards to be specified.

       -r     Run in restricted mode, disallowing any games to be saved.

       -s     Calculate statistics for the precanned boards, and attempt to
              classify the difficulty of solving the boards. Can be used with
              the -v option.

       -t<filename>
              Set the template file. The file set on the command line will be
              used instead of the default template file.

       -v     Solve precanned boards, writing the solution to standard output.

       <filename>
              Name of the optional file containing precanned boards.

ENVIRONMENT
       No environment variables are used directly by the sudoku program.

FILES
       /usr/local/share/sudoku/template
              Template file for generating new sudoku boards.

       /usr/local/share/sudoku/precanned
              Optional file, containing `precanned' sudoku boards.

FILE FORMATS
   /usr/local/share/sudoku/template
       The template file contains a sequence of patterns that are used for
       generating new sudoku boards. Each pattern is started by a line with a
       leading `%' character, and consists of 9 lines of 9 characters. The
       character `.' represents a square that is initially blank, and the
       character `*' represents a square with a digit that is initially
       displayed.

   Compact text format
       This format is similar to that of the template file, but contains
       representations of game boards. Each board is started by a line with a
       leading `%' character, followed by an optional title for the board that
       is displayed when the game is played. This is followed by 9 lines of 9
       characters, where the character `.' represents an initially empty
       square, and the characters `1'-`9' give the value of a fixed board
       square that is initially displayed. The sudoku program can read
       precanned files in this format, and will write them when the -fcompact
       option is set.

   Standard text format
       This format is very similar to the compact text format, but includes
       additional characters to delimit the blocks in the board. The sudoku
       program can read precanned files in this format, and writes them by
       default, unless another output format is set by the -f option.

   Comma separated text format
       This format is useful for importing sudoku boards into a spreadsheet.
       It represents each board by 9 lines of comma separated fields. Each
       field is blank, or contains a digit.  The sudoku program cannot read
       precanned files in this format, and writes them when the -fcsv option
       is set. Unlike the standard or compact text formats, there are no lines
       separating boards, and hence, it is really only feasible to store one
       board per file.

   Postscript format
       This format is useful for printing out sudoku boards. The sudoku
       program cannot read boards stored in this format, and writes them when
       the -fpostscript option is set. Unlike the standard or compact text
       formats, it is not possible to store multiple boards in the same file.

   HTML format
       This format is useful for printing out sudoku boards. The sudoku
       program cannot read boards stored in this format, and writes them when
       the -fhtml option is set. Unlike the standard or compact text formats,
       it is not possible to store multiple boards in the same file.

SEE ALSO
       There are a large number of websites dedicated to the sudoku puzzle
       that can be found easily using a search engine.  Some of these sites
       provide game boards that can be challenging to solve, and others
       provide strategies for finding moves.

DIAGNOSTICS
       There are limited diagnostics available when an error occurs.

ACKNOWLEDGEMENTS
       Mark Foreman for the HTML output format; Joanna Ferris and Heather for
       encouraging this endeavour.

AUTHOR
       Michael Kennett (mike@laurasia.com.au)

COPYRIGHT
       This manual page, and all associated files, have been placed into the
       public domain by Michael Kennett, July 2005. They may be used by
       anybody for any purpose whatsoever, however NO WARRANTY, of any sort,
       applies to this work.





                                                                     SUDOKU(6)
