use strict;
use warnings;
use Test::More;
use Benchmark qw(cmpthese);
use List::Util qw(uniq);

my @first = (1 .. 1000);
my @second = (300 .. 700);

sub slice {
    my %seen;
    @seen{@{$_[0]}, @{$_[1]}} = ();
    return [keys %seen];
}

sub listutil {
    return [uniq(@{$_[0]}, @{$_[1]})];
}

sub seengrep {
    my %seen;
    return [grep {! $seen{$_}++} @{$_[0]}, @{$_[1]}];
}

is_deeply [sort {$a <=> $b} @{slice(   \@first, \@second)}],
          [sort {$a <=> $b} @{listutil(\@first, \@second)}],
          "They matched.";

is_deeply [sort {$a <=> $b} @{listutil(\@first, \@second)}],
          [sort {$a <=> $b} @{seengrep(\@first, \@second)}],
          "They matched again.";

done_testing();

cmpthese (-5, {
    slice    => sub {my $f = slice   (\@first, \@second)},
    listutil => sub {my $f = listutil(\@first, \@second)},
    seengrep => sub {my $f = seengrep(\@first, \@second)},
});