@array = sort @array; # this is optimized by perl as a sort
                      # in place operation that doesn't
                      # require additional memory
my $last = $array[0];
my $i = 1;
while($i<@array) {
  if ($array[$i] eq $last) {
    splice @array, $i, 1
  }
  else {
    $last = $array[$i];
    $i++;
  }
}