Solution to http://blogs.perl.org/users/ovid/2014/12/a-small-puzzle-for-you.html

puzzle.pl

use 5.014;
use warnings;

my @in = (
    [ 'b', 'c', 'f' ],
    [ 'a', 'd'      ],
    [ 'c', 'd', 'e' ],
);

my %indexes = map {; $_ => 1} map @$_, @in;
my $count = scalar keys %indexes;
@indexes{sort keys %indexes} = 0 .. ($count - 1);
my @out = map {
    my @new = (undef) x $count;
    @new[ @indexes{@$_} ] = @$_;
    \@new;
} @in;

use Data::Dumper;
print Dumper \@out;