sub MidLifeXis_bruteforce {
  my $p     = shift;
  my $v     = shift;
  my $check = shift;

  my $worker = sub {
    my $worker   = shift;
    my $prefix   = shift;
    my $tot_size = shift;
    my $places   = shift;
    my $alphabet = shift;
    my $check    = shift;

    my @solution = ( 0, 0 );
    foreach my $letter (@$alphabet) {
      if ($places < 1) {
	return '';
      }
      elsif ($places == 1) {
	@solution = $check->( $prefix . $letter );
	return ( $prefix . $letter ) if ( $solution[1] == $tot_size );
      }
      else {
	my $try = $worker->( $worker,
			     $prefix . $letter,
			     $tot_size,
			     $places - 1,
			     [ grep { $_ ne $letter } @$alphabet ],
			     $check,
			   );
	return $try if $try;
      }
    }
    return '';
  };

  $worker->( $worker,
	     '',
	     $p,
	     $p,
	     [ ( '0' .. '9', 'A' .. 'Z' )[ 0 .. $v - 1 ] ],
	     $check,
	   );
}