use strict;
our %ids;

sub intersect
{
    my %count;
    my @ret;
    my $count = scalar keys %ids;
    foreach my $key (keys %ids) {
        my %this;
        for (@{$ids{$key}}) {
            next if $this{$_};
            $count{$_}++;
            $this{$_}++;
            if ($count{$_} == $count) {
                push @ret, $_;
            }
        }
    }

    undef %ids;
    return @ret;
}


$ids{'foo'} =  [ 3, 4, 4, 5 ];
$ids{'bar'} =  [ 3 ];
$ids{'zoo'} =  [ 3, 4, 5 ];

print "[ ",join(', ',intersect)," ]\n"; # prints "[ 3 ]"