function DrawWinner() public payable {\
  require(drawParticipants.length == requiredParticipants);

  uint blockNo = block.number - 1;
  uint winnerIndex = uint(block.blockhash(blockNo)) % requiredParticipants;

  // This should never happen
  assert(winnerIndex < drawParticipants.length);
  address winner = drawParticipants[winnerIndex];

  // reset the participants so the game can continue - you can do this in solidity
  drawParticipants.length = 0;

  // Pay the winner
  winner.transfer(this.balance);

}