my %inter;
for (keys %hist1)
{
    if (exists $hist2{$_})
    {
        my $val1 = $hist1{$_};
        my $val2 = $hist2{$_};
        $inter{$_} = ($val1 <= $val2) ? $val1 : $val2;
    }
}

##</code><code>##

my @common = grep exists $hist1{$_}, sort keys %hist2;