use strict;
use warnings;

my @letters = qw(a a a b b b c c c);
my @word = qw(a a a b b);

# create the hash
my %count;
for my $letter (@word) { $count{$letter}++ }

my @remain;
for my $letter (@letters) {
	if (not $count{$letter}) {
		push(@remain,$letter);
	}
	else {
		$count{$letter}--;
	}
}
print "@remain\n";

# prints: b c c c