#! perl -slw
use strict;
use Data::Dump qw[ pp ];

sub uniq{ my %x; @x{@_} = (); keys %x }

my @words = do{ local *ARGV = ['words.txt']; <> };
chomp @words;

@words = grep length() > 2, @words;

my %index;

@index{ 'a' .. 'z' } = map chr(0) x int( ( @words + 8 )/8 ), 1 .. 26;

for my $iWords ( 0 .. $#words ) {
    for my $char ( sort uniq split '', $words[ $iWords ] ) {
        vec( $index{ $char }, $iWords, 1 ) = 1;
    }
}

while( chomp( my $given = <STDIN> ) ) {
    my @given = split '', $given;
    my @excludes = grep{ !(1+index $given, $_ ) } 'a'..'z';

    my $mask = chr(0) x int( ( @words + 8 )/8 );

    $mask |= $_ for @index{ @given };
    $mask &= ~ $index{ $_ } for @excludes;

    my $count = unpack "%32b*", $mask;

    print "Found $count words:\n";

    vec( $mask, $_, 1 ) and print $words[ $_ ]
        for 0 .. $#words;

    print "\n\n";
}

__END__
c:\test>790206
fred
Found 30 words:

deed
deeded
deer
def
defer
deferred
deffer
ere
err
erred
fed
fee
feed
feeder
free
freed
freer
red
redder
reed
reef
reefed
reefer
ref
refer
referee
refereed
referred
referrer
reffed