use strict;
use warnings;

my %HoA = (
    flintstones => [qw/fred barney george/],
    jetsons     => [qw/george fred elroy/],
    simpsons    => [qw/fred marge bart barney/]
);


my %d2;
for my $k(keys %HoA){
   for (@{$HoA{$k}}){
      push @{$d2{$_}}, $k;
   }
}
for my $k(sort keys %d2){
   next unless $#{$d2{$k}} >0;
   print "$k:\t (", join (",",sort @{$d2{$k}}),")\n";
}