Sequential Eratosthenes sieve

Sieve.scala

class Sieve(maxNumber: Int) {
  private val candidates = Array.fill(maxNumber + 1)(true)

  def run(): Unit = {
    for (index <- 2 to maxNumber) {
      if (candidates(index)) {
        crossOutMultiples(index)
      }
    }
  }

  private def crossOutMultiples(prime: Int): Unit = {
    println(s"$prime is prime")
    val firstMultiple = prime * 2
    for (index <- firstMultiple to maxNumber by prime) {
      candidates(index) = false
    }
  }
}

object Sieve extends App {
  val start = System.currentTimeMillis()
  new Sieve(maxNumber = 500000).run()
  println(s"Spent just ${System.currentTimeMillis() - start} millis")
}