e49.scala

def isPrime(n: Int): Boolean = (2 to math.sqrt(n).toInt).forall(n % _ != 0)

val groupedPrimes= Stream.from(2).filter(isPrime).dropWhile(_ < 1000).takeWhile(_ < 10000).toList.groupBy(_.toString.sortWith(_ < _))

def findArithmeticProgression(nums: List[Int]): Option[List[Int]] = {
  @annotation.tailrec
  def rec(h: Int, tail: List[Int]): Option[List[Int]] = {
    if (tail.length < 2) return None
    tail.find( n => tail.contains(n + (n - h)) ) match {
      case Some(n) => return Some(List(h, n, n + (n - h)))
      case None    => rec(tail.head, tail.tail)
    }
  }
  rec(nums.head, nums.tail)
}

val result = groupedPrimes.values.map(findArithmeticProgression).collectFirst{ case Some(n) => n }
println(result.get.mkString) // => 296962999629