balance.scala

def balanced(chars: List[Char]): Boolean = {
  def innerBalance(thisChar: Char, rest: List[Char], center: Int): Int = {
    def shift(thisChar: String, center: Int): Int = {
      if (thisChar == "(") {
        center << 1
      } else if (thisChar == ")") {
        center >> 1
      } else {
        center
      }
    }
    if (rest.isEmpty) {
      shift(thisChar.toString, center)
    } else {
      innerBalance(rest.head, rest.tail, shift(thisChar.toString, center))
    }
  }
  innerBalance(chars.head, chars.tail, 1) == 1
}