The Birthday problem (paradox) implementation in Scala. http://en.wikipedia.org/wiki/Birthday_problem

BirthdayParadoxUntilSuccess.scala

package com.liveperson.predictivedialer.examples.misc

import scala.util.Random
import scala.collection.mutable
import com.liveperson.predictivedialer.common.utils.TraversableWithStatistics._

/**
 * Created with IntelliJ IDEA.
 * User: mishaelr
 * Date: 1/16/14
 * Time: 1:47 PM
 */
object BirthdayParadoxUntilSuccess extends App{

  val rand = new Random()

  require(args.length == 2,
    """Birthday Paradox: Usage: there should be two arguments:
      |The total number of "days".
      |The number of experiment repeats.""".stripMargin)

  val (numOfDays, numOfRepeats) = (args(0).toInt, args(1).toInt)
  val experimentsResults = List.fill(numOfRepeats)(numOfBirthdaysUntilCollision)

  println(
    """Birthday Paradox: The mean number of birthdays until collision was %s, the variance was %s.
      |The total number of "days" %s.
      |The number of experiments was %s.
      |sqrt(n) = %s""".format(experimentsResults.mean, experimentsResults.variance, numOfDays, numOfRepeats, math.sqrt(numOfDays)).stripMargin)

  def numOfBirthdaysUntilCollision = {
    val birthdayIterator = Iterator.continually(rand.nextInt(numOfDays)).zipWithIndex
    val encounteredBirthdays = mutable.Set[Int]()
    val firstCollision = birthdayIterator.find{case (birthday, index) => !(encounteredBirthdays add birthday)}
    firstCollision.get._2 + 1 // The +1 is due to index to length
  }
}