use Benchmark qw(:all) ;

my @a;
push @a, int (rand(100)) foreach 1..2_000_000;

my %unique;
my (@awd1, @awd2, @awd3);
cmpthese(5, {
                  'jc' =>
                  sub { foreach my $thingy (@a) { $unique{$thingy} = 1; }
                        @awd1 = keys %unique;
                     },
                  'mk' =>
                  sub { @unique{ @a} = 1;
                        @awd2 = keys %unique;
                     },
                  'ys' =>
                  sub { @unique{ @a} = ();
                        @awd3 = keys %unique;
                     },
                 });