sub generate {
    my $min = shift;
    my @arrays = grep @$_, @_;
    $min -= @arrays;
    return if $min > 0;
    my @current = ("");
    for my $array (@arrays) {
        $min++;
        @current = map {
            my $n = $_;
            length() < $min ? () : $_, map $n.$_, @$array;
        } @current;
    }
    return @current;
}