Select Code to Download

sub permute {
  my @items = @_;
...
    return @items;
  }
}

  15 = 2*3! + 1*2! + 1*1!

sub fb_to_perm {
  my @arr = @{ shift() };
...
  push @ret, @arr;
  return @ret;
}

my $n = 0;
{
...
  ++$n;
  redo;
}

A B C D 000_F   B A C D 100_F   C A B D 200_F   D A B C 300_F
A B D C 001_F   B A D C 101_F   C A D B 201_F   D A C B 301_F
...
A C D B 011_F   B C D A 111_F   C B D A 211_F   D B C A 311_F
A D B C 020_F   B D A C 120_F   C D A B 220_F   D C A B 320_F
A D C B 021_F   B D C A 121_F   C D B A 221_F   D C B A 321_F

A B C D 000_F

...

C D B A 221_F
D A B C 300_F

A B C D 000_F
A C B D 010_F
...
D A B C 300_F
D B A C 310_F
D C A B 320_F

sub offsets {
  my $p = $_[ 0 ];
...

  return ( $i, $d );
}

sub perms {
  my @arr = @_;
...
    redo;
  }
}

    my $j = @arr - $i;
    @arr[ $j+1..$#arr ] = reverse @arr[ $j+1..$#arr ];
    @arr[ $j, $j+$d ] = @arr[ $j+$d, $j ];

    @arr[ 0..$i-1 ] = reverse @arr[ 0..$i-1 ];

    if ( $i % 2 ) {
      @arr[ $i-1, 0 ] = @arr[ 0, $i-1 ];
...
    else {
      @arr[ $i-1, $d-1 ] = @arr[ $d-1, $i-1 ];
    }

Iterator {...}

\sum_{k=0}^{m-1}k*k! = m!-1

(m - 1)*(m - 1)! + (m - 1)! - 1 = m! - 1

sub n_to_fb {
  my ( $n, $m ) = @_;
...
  }
  return $n ? undef : \@fb;
}