Project Euler Problem 14

problem14.scala

  /**
   * http://projecteuler.net/problem=14
   * http://odz.sakura.ne.jp/projecteuler/index.php?cmd=read&page=Problem%2014
   */


  object collatz {
    def apply(i: Int) = calc(i :: Nil).reverse

    private def calc(xs: List[Long]): List[Long] = {
      xs.head match {
        case 1 => xs
        case n if (n % 2 == 0) => calc(n / 2 :: xs)
        case n => calc((n * 3) + 1 :: xs)
      }
    }
  }

  val ret = (1 until 1000000).map(n => (n, collatz(n).size)).sortBy(_._2).last._1
  
  println(ret)