ChargingChaos.scala

object ChargingChaos extends App {

  def flippedSwitch(outlets: Set[BigInt], devices: Set[BigInt]): Option[Int] = {

    val list = outlets.toList map { outlet =>
      devices.map(outlet ^ _)
    }

    val result = (list.head /: list.tail)(_ & _)

    if (result.isEmpty) None else Some(result.map(_.bitCount).min)

  }

  implicit def strToBigIntSet(s: String): Set[BigInt] = s.split(' ').map(BigInt(_, 2)).toSet

  def process(iter: Iterator[String])(pr: String => Unit) =
    for (i <- 1 to iter.next().toInt) yield {
      val Array(n, l) = iter.next() split ' '
      pr(s"Case #$i: ${flippedSwitch(iter.next(), iter.next()).getOrElse("NOT POSSIBLE")}")
    }

  import java.io._
  val out = new PrintStream(new File("a.out"))
  try {
    process(io.Source.fromFile("A-large-practice.in").getLines) { s: String =>
      out.println(s)
    }
  } finally {
    out.flush; out.close
  }

}