in tutorials/tutorial4-completed/TicTacToe/RandomWin/RandomWinInteractor.swift [58:65]
func determineWinner() {
let random = arc4random_uniform(100)
let winner = random > 50 ? PlayerType.player1 : PlayerType.player2
presenter.announce(winner: winner) {
self.mutableScoreStream.updateScore(with: winner)
self.listener?.didRandomlyWin(with: winner)
}
}