Fritz Mehner > Games-Sudoku-Solver > Games::Sudoku::Solver

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Module Version: 1.1.0   Source  

NAME ^

Games::Sudoku::Solver - Solve 9x9-Sudokus recursively.

VERSION ^

This document describes Games::Sudoku::Solver version 1.0.0

SYNOPSIS ^

    use Games::Sudoku::Solver qw(:Minimal set_solution_max count_occupied_cells);

    # specify a Sudoku as flat array (this one has 10 solutions)

    my @sudoku_raw = qw(
        0 4 0 0 2 0 9 0 0
        0 0 0 0 0 0 0 1 0
        0 0 0 0 0 6 8 5 0
        5 8 2 3 0 0 7 0 0
        0 0 0 8 0 7 0 0 0
        0 0 9 0 0 5 1 3 8
        0 9 7 1 0 0 0 0 0
        0 2 0 0 0 0 0 0 0
        0 0 4 0 3 0 0 0 0
    );

    my @sudoku;                                     # the Sudoku data structure
    my @solution;                                   # the solution data structure

    sudoku_set( \@sudoku, \@sudoku_raw );           # convert raw to internal representation

    print "\n===== Sudoku =====\n";
    sudoku_print( \@sudoku );                       # print the Sudoku


    my  $cells_occupied = count_occupied_cells( \@sudoku ); # some statistics
    print "\n", $cells_occupied, " cells occupied, ",
             81-$cells_occupied, " cells free\n";

    set_solution_max(4);                            # stop having 4 solutions found

    my $solutions = sudoku_solve( \@sudoku, \@solution);    # solve the Sudoku

    foreach my $n ( 1..$solutions ) {               # print the solutions
        print "\n--- solution $n ---\n";
        sudoku_print( $solution[$n-1] );
    }

DESCRIPTION ^

This module solves 9x9-Sudoku puzzles by recursion. There is no restriction to the difficulty and the number of solutions.

The puzzle can be stored in a single dimension array or in a file, where unknown cells are presented by zeros or points.

Algorithm

Solving Sudokus is perfectly suited for the application of a recursive algorithm. The basic idea: Find the first free cell, insert an allowed value and get a new Sudoku with one free cell less or a solution if it is complete. In more details:

  1. Build the list of free cells starting from the upper left corner. Set an index on the first free cell.
  2. Build the set of allowed (and until now unused) values for the actual cell by inspecting the according row, column and submatrix.
    • If there exists an allowed values and the Sudoku is complete a solution is found. Discard this value for this cell from the set of allowed values. Go to step 2.
    • If there exists an allowed values and the Sudoku is not complete go ahead to the next free cell in the list of free cells. Go to step 2.
    • If there exists no allowed value free the actual cell and go back one position in the list of free cells. Go to step 2.

The algorithm walks through a tree of mostly incomplete Sudokus. The leaves which are complete are solutions (if any).

SUBROUTINES/METHODS ^

There are two export tags. Minimal exports sudoku_set, sudoku_solve, and sudoku_print. All exports all subroutines described below.

count_occupied_cells

      PURPOSE:  count actually occupied cells
   PARAMETERS:  (1) reference to a Sudoku (array of arrays)
      RETURNS:  number of occupied cells

get_solution_max

      PURPOSE:  get maximal number of solutions to search for
   PARAMETERS:  ---
      RETURNS:  maximal number of solutions to search for

set_solution_max

      PURPOSE:  set maximal number of solutions to search for
   PARAMETERS:  postive number (postive sign allowed)
      RETURNS:  ---

sudoku_check

      PURPOSE:  Check Sudoku for correctness
  DESCRIPTION:  - check rows,  columns
                - check submatrices; numbering:
                      +---+---+---+
                      | 1 | 2 | 3 |
                      +---+---+---+
                      | 4 | 5 | 6 |
                      +---+---+---+
                      | 7 | 8 | 9 |
                      +---+---+---+
                Die of error (croak) if Sudoku is not correct.
   PARAMETERS:  (1) reference to a Sudoku (array of arrays)
      RETURNS:  ---

sudoku_print

      PURPOSE:  print Sudoku
  DESCRIPTION:  Simple text output
   PARAMETERS:  (1) reference to a Sudoku (array of arrays)
      RETURNS:  ---

sudoku_read

      PURPOSE:  read a Sudoku from a file; check format
   PARAMETERS:  (1) reference to a Sudoku (array of arrays)
                (2) name of the input file (scalar)
      RETURNS:  ---

    There a two file formats. Format 1 specifies empty cells with 0.
    The cells are separated by whitespaces. Perl comments are allowed
    on separate lines:

        # 1 solution
         0 3 0 2 6 7 0 4 0
         1 0 0 0 0 0 0 0 5
         7 4 0 5 0 1 0 9 2
         9 0 5 0 0 0 1 0 3
         6 0 0 0 5 0 0 0 8
         8 0 4 0 0 0 7 0 9
         2 9 0 7 0 4 0 8 6
         3 0 0 0 0 0 0 0 4
         0 5 0 6 1 2 0 3 0

    The second format uses points for the empty cells. Separating whitespaces
    are not allowed:

         # 1 solution
         3.4...6.2
         9..627..4
         6..1.4..7
         249...731
         16.....85
         .83...46.
         7..8.5..3
         ...263...
         8.5...9.6

    There is no restriction on the number of empty cells.
    A completely empty Sudokus would generate all possible solutions:

         # 6.670.903.752.021.072.936.960 solutions
         #
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0
         0 0 0 0 0 0 0 0 0

sudoku_set

      PURPOSE:  store the 81 values of a Sudoku from a flat array into
                the internal representation (array of arrays)
   PARAMETERS:  (1) reference to a Sudoku (array of arrays)
                (2) reference to flat array of 81 values (digits)
      RETURNS:  ---
     COMMENTS:  The Sudoku will be checked for correctness.

sudoku_solve

  DESCRIPTION:  solve a Sudoku by recursion
   PARAMETERS:  (1) reference to a Sudoku (array of arrays)
                (2) reference to a solution array (array of arrays of arrays)
                (3) restrictions (hash; optional)
      RETURNS:  number of solutions found

Possible restrictions are:

Maximal number of solutions (0=unbound)
    solution_max    => 10
Unique digits on the 1. diagonal (upper-left to lower-right)
    diagonal_ul_lr  =>  0                       # not unique
    diagonal_ul_lr  =>  1                       # unique
Unique digits on the 2. diagonal (lower-left to upper-right)
    diagonal_ll_ur  =>  0                       # not unique
    diagonal_ll_ur  =>  1                       # unique

DIAGNOSTICS ^

error "$0 : failed to open input file $filename : $!\n"

Subroutine sudoku_read could not open the specified file.

error "error in file '$filename', line ${.}.\n"

Subroutine sudoku_read found a format error when reading the specified file.

croak "value repeated in line ${i} \n"

Subroutine sudoku_check found a format error when checking a Sudoku (may be after reading it with sudoku_read).

croak "value repeated in column ${i} \n"

Subroutine sudoku_check found a format error when checking a Sudoku (may be after reading it with sudoku_read).

croak "value repeated in submatrix ${i} \n"

Subroutine sudoku_check found a format error when checking a Sudoku (may be after reading it with sudoku_read).

warning "$0 : failed to close input file $filename : $!\n";

Subroutine sudoku_read could not close the specified file.

CONFIGURATION AND ENVIRONMENT ^

Games::Sudoku::Solver requires no configuration files or environment variables.

DEPENDENCIES ^

    Carp  - warn of errors
    Clone - recursively copy Perl datatypes

INCOMPATIBILITIES ^

None reported.

BUGS AND LIMITATIONS ^

This module can only solve 9x9-Sudokus. No bugs have been reported.

Please report any bugs or feature requests to bug-games-sudoku-solver@rt.cpan.org, or through the web interface at http://rt.cpan.org.

AUTHOR ^

Dr.-Ing. Fritz Mehner <mehner@fh-swf.de>

LICENSE AND COPYRIGHT ^

Copyright (c) 2006-2007, Dr.-Ing. Fritz Mehner <mehner@fh-swf.de>. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

DISCLAIMER OF WARRANTY ^

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

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