My module:

# $Id: mw.pm,v 1.4 2005/01/12 20:20:06 trammell Exp $

package Mystery::Word;

use strict;
use warnings;

sub new {
    my $class = shift;
    my %defaults = (
        size => 5,
        dictfile => '/usr/share/dict/words',
    );
    my %args = (%defaults, @_);
    return bless \%args, $class;
}

sub hint {
    my ($self, %args) = @_;
    $self->{hint} = \%args;
}

sub solve {
    my $self = shift;
    my @keep;
    WORD:
    for (@{ $self->words }) {
        next WORD unless length == $self->{size};
        foreach my $hint (keys %{ $self->{hint} }) {
            next WORD unless
                letters_in_common($_,$hint) == $self->{hint}{ $hint };
        }
        push @keep, $_;
    }
    return @keep;
}

sub words {
    my ($self, $random) = @_;
    unless ($self->{words}) {
        open (my $fh, $self->{dictfile}) or
            die "Can't open dictionary '$self->{dictfile}': $!";
        while (<$fh>) {
            chomp;
            push @{$self->{words}}, $_;
        }
    }
    if ($random) {
        my $i = rand( @{ $self->{words} } );
        return $self->{words}[$i];
    }
    return $self->{words};
}

sub letters_in_common {
    (my $p = lc $_[0]) =~ y/a-z//cd;
    (my $q = lc $_[1]) =~ y/a-z//cd;
    my %p = map { $_, 1 } split //, $p;
    my %q = map { $_, 1 } split //, $q;
    my %common = (%p, %q);
    return (scalar keys %p) + (scalar keys %q) - (scalar keys %common)
+;
}

sub create {
    my $self = $_[0];
    (my $mysteryword = lc $_[1]) =~ y/a-z//cd;
    $self->{size} = length($mysteryword);

# algorithm is:
# 1. choose a random word $r
# 2. determine how many letters ($n) it has in common with $mysterywor
+d
# 3. solve the puzzle with candidate $r => $n
# 4. if the solution has 1 answer ($mysteryword), we're done, otherwis
+e
#    try again

    my %hints;
    my $count;
    {
        $count++;
        warn "Iteration $count" if $self->{debug};
        my $r = $self->words('random');
        my $n = letters_in_common($r,$mysteryword);
        $self->hint( %hints, $r, $n);
        my @s = $self->solve();
        redo unless grep { $_ eq $mysteryword } @s;
        $hints{ $r } = $n;
        redo unless @s == 1;
    }
    return %hints;
}

1;
[download]

Sample usage:

#!/usr/bin/perl -l

use strict;
use warnings;
use mw; 
use Data::Dumper;

my $puzzle = Mystery::Word->new( debug => 1 );
my %hints = $puzzle->create('camel');
print Dumper(\%hints);

# test solution

my $p2 = Mystery::Word->new( size => 5 );
$p2->hint(%hints);
print for $p2->solve();
[download]

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