【実験】1%は100回やっても63%らしい

interface EventResult {
  winning: boolean, // 事象が起こったか
  count: number // 何回目で起こったか、デバッグや結果を眺めるとき用
}

// 1%で起こる事象を100回やる
// 計算的には63%の確率でwinningがtrueになる
function randomEvent100(): EventResult {
  let result: EventResult | null = null
  for (const count of Array(100).keys()) {
    const winning = Math.random() < 0.01
    if (winning) {
      result = { winning, count }
      break
    }
  }
  if (result === null) result = { winning: false, count: 100 }
  return result
}

// 100回やったときに出るかどうかを試行回数分繰り返し、確率にする
function experiment(trials: number) {
  const array = Array(trials).fill(0).map(randomEvent100)
  const probability = array.filter(r => r.winning).length / trials
  return { probability, results: array }
}

const TRIALS = 1000000
const { probability } = experiment(TRIALS)
console.log(`確率: ${probability * 100}% (試行回数: ${TRIALS})`)

case class EventResult(winning: Boolean, count: Int)

def randomEvent = {
  import scala.util.Random
  Random.nextInt(100) == 1
}

def randomEvent100 = {
  val itr = LazyList.continually(randomEvent).take(100)
  EventResult(
    winning = itr.exists(identity),
    count = itr.indexWhere(identity)
  )
}

def experiment(trials: Int): Float = {
  val itr = LazyList.continually(randomEvent100).take(trials)
  itr.count(_.winning).toFloat / trials
}

val TRIALS = 100000
val probability = experiment(TRIALS)
println(s"確率: ${probability * 100}% (試行回数: $TRIALS 回)")