#! perl -w
use strict;
use Benchmark qw(cmpthese);

sub intersect (\@\@) {
    my ($aryRef1, $aryRef2) = @_;
    my %count;
    $count{$_}++ foreach @$aryRef1, @$aryRef2;
    return grep{ $count{$_} == 1 } keys %count;
}

my @array1 = (1 .. 28000);
my @array2 = (1..1000, 1..100); # create some duplicates with duplicates

my %hashBase;
@hashBase{@array1} = undef;

sub faq {
	my @dup = intersect( @array1, @array2 );
}
sub hash {
	my %hashAry;
	@hashAry{@array1} = undef;
    my @dup = delete @hashAry{@array2};
}
sub prehash {
    my %hashAry = %hashBase;
	my @dup = delete @hashAry{@array2};

}
sub hash_lret {
	my %hashAry;
	@hashAry{@array1} = undef;
	my @dup = delete @hashAry{@array2};
    return keys %hashAry;
}

sub prehash_lret {
    my %hashAry = %hashBase;
	my @dup = delete @hashAry{@array2};
	return keys %hashAry;
}

sub grepped {
	my %reject;
	$reject{$_} = 1 for @array2;
    my @clean=grep !$reject{$_}, @array1;
}

cmpthese 100,{
              faq          => \&faq,
              hash         => \&hash,
              prehash      => \&prehash,
              hash_lret    => \&hash_lret,
              prehash_lret => \&prehash_lret,
              grepped      => \&grepped,
             };


##</code><code>##


__END__
Benchmark: timing 100 iterations of faq, grepped, hash, hash_lret, prehash, prehash_lret...
       faq: 35 wallclock secs (34.09 usr +  0.02 sys = 34.11 CPU) @  2.93/s (n=100)
   grepped: 11 wallclock secs ( 9.91 usr +  0.00 sys =  9.91 CPU) @ 10.09/s (n=100)
      hash: 10 wallclock secs (10.27 usr +  0.00 sys = 10.27 CPU) @  9.74/s (n=100)
 hash_lret: 10 wallclock secs (10.23 usr +  0.00 sys = 10.23 CPU) @  9.77/s (n=100)
   prehash: 16 wallclock secs (15.13 usr +  0.00 sys = 15.13 CPU) @  6.61/s (n=100)
prehash_lret: 16 wallclock secs (15.17 usr +  0.00 sys = 15.17 CPU) @  6.59/s (n=100)
               Rate       faq prehash_lret  prehash      hash hash_lret  grepped
faq          2.93/s        --         -56%     -56%      -70%      -70%     -71%
prehash_lret 6.59/s      125%           --      -0%      -32%      -33%     -35%
prehash      6.61/s      126%           0%       --      -32%      -32%     -35%
hash         9.74/s      232%          48%      47%        --       -0%      -4%
hash_lret    9.77/s      233%          48%      48%        0%        --      -3%
grepped      10.1/s      244%          53%      53%        4%        3%       --