FairWarning.scala

import scala.io.Source
import java.io.PrintWriter

object FairWarning {

  val in = Source.fromFile("small.in").getLines
  val out = new PrintWriter("small.out")

  def main(args: Array[String]) {
    val n = in.next.toInt
    val lines = in.take(n).toList
    val rs = lines.map(line => TestCase(line.tail).solve)
    
    rs.zipWithIndex foreach { case (res, idx) => out.println(s"Case #${idx + 1}: $res") }
    
    out.flush()
  }

  case class TestCase(_line: String) {

    def secList = (_line split (" ")).tail map (BigInt(_))

    def solve = {
      val first = secList.head
      val subs = secList.tail.map(x => (first - x).abs).filterNot(_ == 0)
      val gcd = subs.foldLeft(subs.head)(_ gcd _)
      val res = gcd - first % gcd
      if (res == first || res == BigInt("1")) 0 else res
    }
  }

}