sub score {
    my ($str, $array) = @_;
    my $vec = "\0" x length($str);
    for (@$array) {
        my $idx = index $str, $_;
        # Matching substrings are padded into position with nulls
        $vec |= ("\0" x $idx) . $_;
    }
    # Matching characters become nulls; others non-nulls
    $vec ^= $str;
    # Count nulls
    $vec =~ tr/\0//;
}