my %revhash;
while (my($k, $v) = each %hash) {
  push @{$revhash{$v}}, $k;
}
for my $val (sort { $a <=> $b } keys %revhash) {
  my @keys = @{$revhash{$_}};
  if (@keys > 1) { # only items where there's a tie
    print "$val is shared by @keys\n";
  }
}