# warning: untested
my %collection;
while(<ALBUMS>) {
   my ($artist, $album, $song) = split;
   push @{$collection{$artist}{$album}}, $song;
}

##</code><code>##

foreach my $artist (keys %collection) {
   print "$artist:\n";
   foreach my $album (keys %{$collection{$artist}}) {
      print "\t$album:\n\t\t";
      print join("\n\t\t", @{$collection{$artist}{$album}}), "\n";
   }
}