my @minima;
  my @maxima;
  my $prev_cmp = 0;

  for (0 .. $#array - 1) {
    my $cmp = $array[$_] <=> $array[$_+1];
    if ($cmp != $prev_cmp) {
      push @minima, $array[$_] if $cmp < 0;
      push @maxima, $array[$_] if $cmp > 0;
      # when this and next elements are ==, defer checking for
      # minima/maxima till next loop iteration
      $prev_cmp = $cmp if $cmp;
    }
  }
  if (@array) {
    push @minima, $array[-1] if $prev_cmp >= 0;
    push @maxima, $array[-1] if $prev_cmp <= 0;
  }