use strict;
use warnings;
use Benchmark;

Benchmark::cmpthese(-1,{
   'shift' => sub {
      my (%seen, $string);
      my @array = (0..1000, 0..1000);
      $seen{$string}++ while $string = shift @array;
      for (keys %seen) {
         push @array, $_;
         delete $seen{$_};
      }
   },
   'grep'  => sub {
      my %seen;
      my @array = (0..1000, 0..1000);
      my @unique = grep { ! $seen{$_}++ } @array;
   },
});