Yet another way, not necessarily the best way: 
my @arr1 = qw(a b b c d);
my @arr2 = qw(c c d e e f);

my ($unique1, $common, $unique2) = common_unique(\@arr1, \@arr2);

sub common_unique {
 my (@u_c, %union);
 exists $union{$_} or $union{$_}-- for @{$_[0]};
 no warnings 'uninitialized';
 $union{$_} <= 0 and $union{$_}++ for @{$_[1]};
 while (my ($key, $value) = each %union) {
  push @{$u_c[$value+1]}, $key;
 }
 return @u_c;
}

[download]
Updated.

In reply to Re: Efficient Comparison of Array elements by runrig
in thread Efficient Comparison of Array elements by aging acolyte

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