sub consensus {
  my $len = length($_[0]);  # all strands are of one length, right?
  my @cons;

  # loop over the positions in the strands
  for my $i (0 .. $len - 1) {
    my %freq;
    my $max = 0;

    # loop over character $i in each of the strands
    for (map substr($_, $i, 1), @_) {
      $freq{$_}++;

      # save the max value
      $max = $freq{$_} if $freq{$_} > $max;
    }

    # store only those who occur the most times
    push @cons, [grep $freq{$_} == $max, keys %freq];
  }

  return \@cons;
}