Project Euler: Problem 10

euler.scala

package euler.zerosum {

  package object Sieve {
    /**
     * Int型エラトステネスの篩
     */
    def sieveInt(numbers: List[Int]): List[Int] = {
      sieveInt(numbers, Nil)
    }

    private def sieveInt(numbers: List[Int], primes: List[Int]): List[Int] = {
      if(primes.nonEmpty && Math.pow(primes.last, 2) > numbers.last) {
        primes ::: numbers
      } else {
        val h = numbers.head
        sieveInt(numbers.tail.filter(_%h != 0), primes ::: h :: Nil)
      }
    }

    /**
     * Long型エラトステネスの篩
     */
    def sieveLong(numbers: List[Long]): List[Long] = {
      sieveLong(numbers, Nil)
    }

    private def sieveLong(numbers: List[Long], primes: List[Long]): List[Long] = {
      if(primes.nonEmpty && Math.pow(primes.last, 2) > numbers.last) {
        primes ::: numbers
      } else {
        val h = numbers.head
        sieveLong(numbers.tail.filter(_%h != 0), primes ::: h :: Nil)
      }
    }
  }

  package object Time {
    def printExecuteTime(proc: => Unit) = {
      val start = System.currentTimeMillis
      proc
      println((System.currentTimeMillis - start) + " msec")
    }
  }
}

Euler0010.scala

/*
 * $ scalac -cp . euler.scala Euler0010.scala
 * $ scala Euler0010 <arg: Int>
 */
import euler.zerosum.Sieve._
import euler.zerosum.Time._

object Euler0010 {

  private def execute(max: Long): Long = {
    sieveLong((2L to max).toList).sum
  }

  def main(args: Array[String]) {
    printExecuteTime {
      println(execute(args(0).toLong))
    }
  }
}