Games::LMSolve::Base - base class for puzzle solvers.

Games-LMSolve documentation Contained in the Games-LMSolve distribution.

Index

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NAME

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Games::LMSolve::Base - base class for puzzle solvers.

SYNOPSIS

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    package MyPuzzle::Solver;

    use Games::LMSolve::Base;

    @ISA = qw(Games::LMSolve::Base);

    # Override these methods:

    sub input_board { ... }
    sub pack_state { ... }
    sub unpack_state { ... }
    sub display_state { ... }
    sub check_if_final_state { ... }
    sub enumerate_moves { ... }
    sub perform_move { ... }

    # Optionally: 
    sub render_move { ... }
    sub check_if_unsolvable { ... }

    package main;

    my $self = MyPuzzle::Solver->new();

    $self->solve_board($filename);

DESCRIPTION

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This class implements a generic solver for single player games. In order to use it, one must inherit from it and implement some abstract methods. Afterwards, its interface functions can be invoked to actually solve the game.

METHODS

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new()

The constructor.

$self->initialize()

Should be inherited to implement the construction.

$self->main()

Actually solve the board based on the arguments in the command line.

METHODS TO OVERRIDE

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input_board($self, $file_spec)

This method is responsible to read the "board" (the permanent parameters) of the puzzle and its initial state. It should place the board in the object's keys, and return the initial state. (in unpacked format).

Note that $file_spec can be either a filename (if it's a string) or a reference to a filehandle, or a reference to the text of the board. input_board() should handle all cases.

You can look at the Games::LMSolve::Input module for methods that facilitate inputting a board.

pack_state($self, $state_vector)

This function accepts a state in unpacked form and should return it in packed format. A state in unpacked form can be any perl scalar (as complex as you like). A state in packed form must be a string.

unpack_state($self, $packed_state)

This function accepts a state in a packed form and should return it in its expanded form.

display_state($self, $packed_state)

Accepts a packed state and should return the user-readable string representation of the state.

check_if_final_state($self, $state_vector)

This function should return 1 if the expanded state $state_vector is a final state, and the game is over.

enumerate_moves($self, $state_vector)

This function accepts an expanded state and should return an array of moves that can be performed on this state.

perform_move($self, $state_vector, $move)

This method accepts an expanded state and a move. It should try to peform the move on the state. If it is successful, it should return the new state. Else, it should return undef, to indicate that the move cannot be performed.

check_if_unsolvable($self, $state_vector) (optional over-riding)

This method returns the verdict if $state_vector cannot be solved. This method defaults to returning 0, and it is usually safe to keep it that way.

render_move($self, $move) (optional overriding)

This function returns the user-readable stringified represtantion of a move.

API

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$self->solve_board($file_spec, %args)

Solves the board specification specified in $file_spec. %args specifies optional arguments. Currently there is one: 'max_iters' that specifies the maximal iterations to run.

Returns whatever run_scan returns.

$self->run_scan(%args)

Continues the current scan. %args may contain the 'max_iters' parameter to specify a maximal iterations limit.

Returns two values. The first is a progress indicator. "solved" means the puzzle was solved. "unsolved" means that all the states were covered and the puzzle was proven to be unsolvable. "interrupted" means that the scan was interrupted in the middle, and could be proved to be either solvable or unsolvable.

The second argument is the final state and is valid only if the progress value is "solved".

$self->get_num_iters()

Retrieves the current number of iterations.

$self->display_solution($progress_code, $final_state)

If you input this message with the return value of run_scan() you'll get a nice output of the moves to stdout.

$self->set_run_time_states_display(\&states_display_callback)

Sets the run time states display callback to \&states_display_callback.

This display callback accepts a reference to the solver and also the following arguments in key => value pairs:

"state" - the expanded state. "depth" - the depth of the state. "move" - the move leading to this state from its parent.

SEE ALSO

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Games::LMSolve::Input

AUTHORS

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Shlomi Fish, http://www.shlomifish.org/

Games-LMSolve documentation Contained in the Games-LMSolve distribution. 
package Games::LMSolve::Base;

use strict;
use warnings;

use Getopt::Long;

use vars qw($VERSION);

$VERSION = '0.8.4';

use Exporter;

use vars qw(@ISA @EXPORT_OK);

@ISA=qw(Exporter);

@EXPORT_OK=qw(%cell_dirs);

use vars qw(%cell_dirs);

%cell_dirs = 
    (
        'N' => [0,-1],
        'NW' => [-1,-1],
        'NE' => [1,-1],
        'S' => [0,1],
        'SE' => [1,1],
        'SW' => [-1,1],
        'E' => [1,0],
        'W' => [-1,0],
    );


sub new
{
    my $class = shift;

    my $self = {};

    bless $self, $class;

    $self->initialize(@_);

    return $self;    
}

sub initialize
{
    my $self = shift;

    $self->{'state_collection'} = { };
    $self->{'cmd_line'} = { 'scan' => "brfs", };

    $self->{'num_iters'} = 0;

    return 0;
}


my %scan_functions =
(
    'dfs' => sub {
        my $self = shift;

        return $self->_solve_brfs_or_dfs(1, @_);
    },
    'brfs' => sub {
        my $self = shift;

        return $self->_solve_brfs_or_dfs(0, @_);
    },
);

sub main
{
    my $self = shift;

    # This is a flag that specifies whether to present the moves in Run-Length
    # Encoding.
    my $to_rle = 1;
    my $output_states = 0;
    my $scan = "brfs";
    my $run_time_states_display = 0;

    #my $p = Getopt::Long::Parser->new();
    if (! GetOptions('rle!' => \$to_rle, 
        'output-states!' => \$output_states,
        'method=s' => \$scan,
        'rtd!' => \$run_time_states_display,
        ))
    {
        die "Incorrect options passed!\n"
    }

    if (!exists($scan_functions{$scan}))
    {
        die "Unknown scan \"$scan\"!\n";
    }

    $self->{'cmd_line'}->{'to_rle'} = $to_rle;
    $self->{'cmd_line'}->{'output_states'} = $output_states;
    $self->{'cmd_line'}->{'scan'} = $scan;
    $self->set_run_time_states_display($run_time_states_display && \&_default_rtd_callback);

    my $filename = shift(@ARGV) || "board.txt";

    my @ret = $self->solve_board($filename);

    $self->display_solution(@ret);
}



    



sub _die_on_abstract_function
{
    my ($package, $filename, $line, $subroutine, $hasargs,
        $wantarray, $evaltext, $is_require, $hints, $bitmask) = caller(1);
    die ("The abstract function $subroutine() was " . 
        "called, while it needs to be overrided by the derived class.\n");
}


sub input_board
{
    return _die_on_abstract_function();
}


# A function that accepts the expanded state (as an array ref)
# and returns an atom that represents it.
sub pack_state
{
    return _die_on_abstract_function();
}


# A function that accepts an atom that represents a state 
# and returns an array ref that represents it.
sub unpack_state
{
    return _die_on_abstract_function();
}


# Accept an atom that represents a state and output a 
# user-readable string that describes it.
sub display_state
{
    return _die_on_abstract_function();
}


sub check_if_final_state
{
    return _die_on_abstract_function();
}


# This function enumerates the moves accessible to the state.
# If it returns a move, it still does not mean that this move is a valid 
# one. I.e: it is possible that it is illegal to perform it.
sub enumerate_moves
{
    return _die_on_abstract_function();
}


# This function accepts a state and a move. It tries to perform the
# move on the state. If it is succesful, it returns the new state.
#
# Else, it returns undef to indicate that the move is not possible.
sub perform_move
{
    return _die_on_abstract_function();
}


# This function checks if a state it receives as an argument is a
# dead-end one.
sub check_if_unsolvable
{
    return 0;
}


# This is a function that should be overrided in case
# rendering the move into a string is non-trivial.
sub render_move
{
    my $self = shift;

    my $move = shift;

    return defined($move)?$move:"";
}


sub _solve_brfs_or_dfs
{
    my $self = shift;
    my $state_collection = $self->{'state_collection'};
    my $is_dfs = shift;
    my %args = @_;
    
    my $run_time_display = $self->{'cmd_line'}->{'rt_states_display'};
    my $rtd_callback = $self->{'run_time_display_callback'};
    my $max_iters = $args{'max_iters'} || (-1);
    my $check_iters = ($max_iters >= 0);
    
    my (@queue, $state, $coords, $depth, @moves, $new_state);

    if (exists($args{'initial_state'}))
    {
        push @queue, $args{'initial_state'};
    }

    my @ret;

    @ret = ("unsolved", undef);

    while (scalar(@queue))
    {
        if ($check_iters && ($max_iters <= $self->{'num_iters'}))
        {
            @ret = ("interrupted", undef);
            goto Return;
        }
        if ($is_dfs)
        {
            $state = pop(@queue);
        }
        else
        {
            $state = shift(@queue);
        }
        $coords = $self->unpack_state($state);
        $depth = $state_collection->{$state}->{'d'};

        $self->{'num_iters'}++;

        # Output the current state to the screen, assuming this option
        # is set.
        if ($run_time_display)
        {
            $rtd_callback->(
                $self,
                'depth' => $depth,
                'state' => $coords,
                'move' => $state_collection->{$state}->{'m'},
            );
            # print ((" " x $depth) . join(",", @$coords) . " M=" . $self->render_move($state_collection->{$state}->{'m'}) ."\n");
        }
        
        if ($self->check_if_unsolvable($coords))
        {
            next;
        }

        if ($self->check_if_final_state($coords))
        {
            @ret = ("solved", $state);
            goto Return;
        }
        
        @moves = $self->enumerate_moves($coords);

        foreach my $m (@moves)
        {
            my $new_coords = $self->perform_move($coords, $m);
            # Check if this move leads nowhere and if so - skip to the next move.
            if (!defined($new_coords))
            {
                next;
            }
            
            $new_state = $self->pack_state($new_coords);
            if (! exists($state_collection->{$new_state}))
            {
                $state_collection->{$new_state} = 
                    {
                        'p' => $state, 
                        'm' => $m, 
                        'd' => ($depth+1)
                    };
                push @queue, $new_state;
            }
        }
    }    
    
    Return:

    return @ret;
}

sub _run_length_encoding
{
    my @moves = @_;
    my @ret = ();

    my $prev_m = shift(@moves);
    my $count = 1;
    my $m;
    while ($m = shift(@moves))
    {
        if ($m eq $prev_m)
        {
            $count++;            
        }
        else
        {
            push @ret, [ $prev_m, $count];
            $prev_m = $m;
            $count = 1;
        }
    }
    push @ret, [$prev_m, $count];

    return @ret;    
}


sub _solve_state
{
    my $self = shift;
    
    my $initial_coords = shift;
    
    my $state = $self->pack_state($initial_coords);
    $self->{'state_collection'}->{$state} = {'p' => undef, 'd' => 0};

    return 
        $self->run_scan(
            'initial_state' => $state,
            @_
        );
}


sub solve_board
{
    my $self = shift;
    
    my $filename = shift;

    my $initial_coords = $self->input_board($filename);

    return $self->_solve_state($initial_coords, @_);
}


sub run_scan
{
    my $self = shift;

    my %args = @_;

    return 
        $scan_functions{$self->{'cmd_line'}->{'scan'}}->(
            $self,
            %args
        );
}


sub get_num_iters
{
    my $self = shift;

    return $self->{'num_iters'};
}


sub display_solution
{
    my $self = shift;

    my @ret = @_;

    my $state_collection = $self->{'state_collection'};

    my $output_states = $self->{'cmd_line'}->{'output_states'};
    my $to_rle = $self->{'cmd_line'}->{'to_rle'};

    my $echo_state = 
        sub {
            my $state = shift;
            return $output_states ? 
                ($self->display_state($state) . ": Move = ") :
                "";
        };    

    print $ret[0], "\n";

    if ($ret[0] eq "solved")
    {
        my $key = $ret[1];
        my $s = $state_collection->{$key};
        my @moves = ();
        my @states = ($key);

        while ($s->{'p'})
        {
            push @moves, $s->{'m'};
            $key = $s->{'p'};
            $s = $state_collection->{$key};
            push @states, $key;
        }
        @moves = reverse(@moves);
        @states = reverse(@states);
        my $num_state;
        if ($to_rle)
        {
            my @moves_rle = _run_length_encoding(@moves);
            my ($m);

            $num_state = 0;
            foreach $m (@moves_rle)
            {
                print $echo_state->($states[$num_state]) . $self->render_move($m->[0]) . " * " . $m->[1] . "\n";
                $num_state += $m->[1];
            }
        }
        else
        {
            for($num_state=0;$num_state<scalar(@moves);$num_state++)
            {
                print $echo_state->($states[$num_state]) . $self->render_move($moves[$num_state]) . "\n";
            }            
        }
        if ($output_states)
        {
            print $self->display_state($states[$num_state]), "\n";
        }
    }
}

sub _default_rtd_callback
{
    my $self = shift;

    my %args = @_;
    print ((" " x $args{depth}) . join(",", @{$args{state}}) . " M=" . $self->render_move($args{move}) ."\n");
}


sub set_run_time_states_display
{
    my $self = shift;
    my $states_display = shift;

    if (! $states_display)
    {
        $self->{'cmd_line'}->{'rt_states_display'} = undef;
    }
    else
    {
        $self->{'cmd_line'}->{'rt_states_display'} = 1;
        $self->{'run_time_display_callback'} = $states_display;
    }

    return 0;
}


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