use strict;
use warnings;
use List::Util 'uniq';
use Test::More;

my @input  = (1,2,2,3,4,5,2,1);
my @wanted = (1,2,3,4,5);

my @got = uniq @input;

is_deeply(\@got, \@wanted);

done_testing;
__END__
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Hope this helps!