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

ovid-puzzle.pl

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

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

my $i = 0;
my %map;
foreach my $k (sort @a, @b, @c) {
    $map{$k} //= $i++;
}

my (@newa, @newb, @newc);
@newa[$i-1, @map{@a}] = (undef, @a);
@newb[$i-1, @map{@b}] = (undef, @b);
@newc[$i-1, @map{@c}] = (undef, @c);

print Dumper \@newa, \@newb, \@newc;