[Project Euler] Problem 20

Problem 20

BigIntegerを使うだけ。

object P020 {
  def main(args:Array[String]) {
    def fact(n:Int):BigInt = n match {
      case 0 => new BigInt(java.math.BigInteger.ONE)
      case _ => new BigInt(java.math.BigInteger.valueOf(n))*fact(n-1)
    }
    val r = fact(100).toString.toCharArray.map{c => c-'0'}.foldLeft(0)(_+_)
    println(r)
  }
}