meetup-20170118

kats2.scala

// https://projecteuler.net/problem=8

// ---------- LargestProduct.scala ----------
import scala.annotation.tailrec

object LargestProduct {

  def solution(s: String, magnitude: Int): Long = {

    def charToLong(c: Char): Long = c.toLong - 48L

    def product(l: List[Long]):Long = l.foldLeft(1L)(_ * _)

    @tailrec
    def iterate(frame: List[Long], rest: List[Char], max: Long): Long = rest match {
      case Nil => max
      case x::xs => {
        val newFrame: List[Long] = frame.tail :+ charToLong(x)
        val newMax = product(newFrame)
        iterate(newFrame, xs, Math.max(newMax, max))
      }
    }

    val (initFrame, initRest) = s.splitAt(magnitude)
    val initFrameLong: List[Long] = initFrame.toList map charToLong
    val initMax = product(initFrameLong)

    iterate(initFrameLong, initRest.toList, initMax)
  }

}

// ---------- LargestProductSpec.scala ----------
import org.scalatest.FunSpec

class LargestProductSpec extends FunSpec {

  import  LargestProduct._

  val testData: Seq[((String, Int), Long)] = Seq(
    (("1111111112", 3), 2L),
    (("7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450", 13), 23514624000L)
  )

  for(t <- testData) {
    it(s"should return ${t._2} for ${t._1}") {
      assert(solution(t._1._1, t._1._2) === t._2)
    }
  }

}