SimpleDiceHistogrammer.scala

import scala.util.Random.nextInt

/**
 Simulate throwing two six-sided dice 200 times and create a histogram of the results like this:
 
 2: XXXX
 3: XXXXXXXXXX
 4: XXXXXXXXXXXXXXXXXXXXXX
 5: XXXXXXXXXXXXXXXXXXXXX
 6: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 7: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 8: XXXXXXXXXXXXXXXXXXXXXXXXXX
 9: XXXXXXXXXXXXXXXXXXXXX
10: XXXXXXXXXXXXXX
11: XXXXXXXXXXXX
12: XXXX
**/

object SimpleDiceHistogrammer extends App {
  println(DiceHist.roll(200))
}

trait DiceHist {
  def roll(): DiceHist
}

object DiceHist {
  private val IndOffset = 2
  private val NRows = 11
  
  private def apply(rolls: IndexedSeq[String]) = new DiceHistImpl(rolls)  
  
  private def empty: DiceHist = 
    DiceHist(IndexedSeq.tabulate(NRows) { i => f"${i + IndOffset}%2d: " })

  def roll(times: Int): DiceHist =
    (1 to times).foldLeft(empty) { (hist, _) =>
      hist.roll()
  }

  private class DiceHistImpl(rolls: IndexedSeq[String]) extends DiceHist {   
    def roll(): DiceHist = {
      val rollRes = Dice.roll() + Dice.roll()
      val i = rollRes - IndOffset
      DiceHist(rolls updated (i, rolls(i) + 'X'))
    }

    override def toString = rolls mkString "\n"
  }
}
  
object Dice {
  def roll(): Int = nextInt(6) + 1
}