SnapperChain.scala

object SnapperChain extends App {

  def state(n: Int, k: Int): Boolean =
    BigInt(k + 1) % (BigInt(2) pow n) == 0

  def process(lineIn: Iterator[String])(lineOut: String => Unit) = {

    for (i <- 1 to lineIn.next().toInt) {

      val Array(n, k) = lineIn.next() split ' ' map (_.toInt)

      lineOut(s"Case #$i: ${if (state(n, k)) "ON" else "OFF"}")
    }
  }

  val writer = new java.io.PrintWriter("a.large.out")
  try {
    process(io.Source.fromFile("A-large-practice.in").getLines)(writer.println)
  } finally {
    writer.flush(); writer.close()
  }

}

SnapperChainTest.scala

import SnapperChain._

class SnapperChainTest extends FunSuite {


  test("sample #1") {
    assert(state(1,0) === false)
  }
  
  test("sample #2") {
    assert(state(1,1) === true)
  }
  
  test("sample #4") {
    assert(state(4,47) === true)
  }
  
  
  test("sample case") {
    val input = """4
1 0
1 1
4 0
4 47""".lines

    val expected = """Case #1: OFF
Case #2: ON
Case #3: OFF
Case #4: ON""".lines

    process(input) { s =>
      for (line <- s.lines)
        assert(line === expected.next())
    }
  }

  test("full small case") {
    val input = io.Source.fromFile("A-small-practice.in").getLines()
    val expected = io.Source.fromFile("a.small.out.ref").getLines()

    process(input) { s =>
      for (line <- s.lines)
        assert(line.trim === expected.next().trim)
    }
  }

  test("full large case") {
    val input = io.Source.fromFile("A-large-practice.in").getLines()
    val expected = io.Source.fromFile("a.large.out.ref").getLines()

    process(input) { s =>
      for (line <- s.lines)
        assert(line.trim === expected.next().trim)
    }
  }
}