use Algorithm::FastPermute;

sub tux_a_fp {
    my ($length, $ones) = @_;
    my @l = ((0) x ($length - $ones), (1) x $ones);
    my %seen;
    permute { $seen{join "" => @l}++ } @l;
    [ keys %seen ];
    }

sub tux_for {
    my ($length, $ones) = @_;
    my $s1 = "1" x $ones;
    my $s0 = "0" x ($length - $ones);
    [   map  { substr unpack ("b*", $_), 0, $length }
        grep { $ones == unpack "%32b*" => $_ }
        map  { pack "L<", $_ }
        oct "0b$s1" .. oct "0b$s1$s0"
        ];
    }

sub tux_tr {
    my ($length, $ones) = @_;
    my $s1 = "1" x $ones;
    my $s0 = "0" x ($length - $ones);
    [   grep { $ones == tr/1/1/ }
        map  { substr unpack ("b*", pack "L<",$_), 0, $length }
        oct "0b$s1" .. oct "0b$s1$s0"
        ];
    }