sub pick_n
  {
    my($n,$from,$to) = @_;
    my(@picked);

    for(my $i=$from;$i<=$to;$i++)
      {
        if(rand(1) <= ($n/($to-$i+1)))
          {
            push(@picked,$i);
            $n--;
          }
      }
    return @picked;
  }