sub genRegex{
	my $word = shift;

	my $re = '(.)';
	my @c =  split '', $word ;
	for my $c ( 1 .. $#c ) {
		my $match = 1+index $word, $c[$i], 0;
		$re .= $match <= $c[$i] 
		     ? '($' . ($match - 1) . ')'
		     : '([^$' . join( '$', 1..$i ) . '])';
		}
	}
	return qr[$re];
}
...

# Build a hash relating cryptoword with a regex to find possible matches.
$soln{$_}{regex} = genRegex $_ for @crypts;

open WORDS, '<words.txt' or die $!;

# build an HoA of all the possible matches
while( chomp( my $word = <WORDS> ) ) {
	print $word;
	for( keys %soln ) {
		push @{ $soln{ $_ }{ possibles } }, $word
			if $word =~ $soln{$_}{regex};
	}
}