import scala.annotation.tailrec

def countTrue(bools: List[Boolean]): Int = {
  bools.foldLeft(0)((n, bool) => if (bool) n + 1 else n)
}

countTrue(List(true, true, false, true, false, false))

def remDup[T](list: List[T]): List[T] = {
  list.foldRight(List.empty[T])((elem: T, res: List[T]) => {
    if (res.contains(elem)) res
    else elem::res
  })
}

def remDup2[T](list: List[T]): List[T] = {
  list.foldLeft(List.empty[T])((res: List[T], elem: T) => {
    if (res.contains(elem)) res
    else res :+ elem
  })
}

def remDup3[T](list: List[T]): List[T] = {
  @tailrec
  def helper(list: List[T], distinct: List[T]): List[T] = {
    list match {
      case head::rest if distinct.contains(head) => helper(rest, distinct)
      case head::rest => helper(rest, distinct :+ head)
      case Nil => distinct
    }
  }
  helper(list, List.empty[T])
}

remDup(List(5,3,2,4,3,2,3,3)) // List(5,3,2,4)
remDup(List("hello", "youpi", "hello", "hello")) // List("hello", "youpi")