#!/usr/bin/perl
use strict;
use warnings;

my $file = $ARGV[0] || 'TWL06.txt';
open(my $fh, '<', $file) or die "Unable to open '$file' for reading: $!";

my @word;
while (<$fh>) {
    chomp;
    next if length($_) < 3 || /[^a-zA-Z]/;
    push @word, lc($_);
}

my %index;
for ('a' .. 'z') {
    # Bitstring long enough to represent all words - all bits set to 0
    $index{$_} = chr(0) x int((@word + 8) / 8);
}

# For each unique char in every word
# Set the bit corresponding to the index of the word to 1
for my $idx (0 .. $#word) {
    my %seen;
    for my $chr (sort split //, $word[$idx]) {
        vec($index{$chr}, $idx, 1) = 1 if ! $seen{$chr}++;
    }
}

print "Please enter an input string: ";
chomp(my $input = <STDIN>);

my @include = split //, $input;
my @exclude = grep {! (1 + index($input, $_))} 'a' .. 'z'; # list of letters not in input string

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

# Turn on bits for all words that have at least 1 letter in common with input string 
$mask |= $_ for @index{@include};

# Turn off bits for any word that contains at least 1 letter not in the input string
for (@exclude) {
    # Words not containing excluded letter (though they may contain letters not in input string)
    my $remain = ~ $index{$_};
    # Words that do not have excluded letter but do have letter in common with input string 
    $mask &= $remain;
}

for my $idx (0 .. $#word) {
    next if ! vec($mask, $idx, 1); # Not even a candidate
    next if ! finalCheck($word[$idx], $input);
    print "$word[$idx]\n";
}

sub finalCheck {
    my ($candidate, $allowed) = @_;
    for (split //, $candidate) {
        $allowed =~ s/$_// or return; # return if the letter does not remain in the candidate list
    }
    return 1;
}