Scala solution to TopCoder problem 'PrimeStatistics': #LearningScala

PrimeStatistics.scala

object PrimeStatistics {
  def isPrime(x:Int):Boolean = {
    if (x==1 || x==2 || x==3) return true
    if (x % 2 == 0) return false
    (3 to math.sqrt(x).toInt by 2).forall(y=>x % y != 0)
  }                                               //> isPrime: (x: Int)Boolean
  
  def mostCommonRemainder(lowerBound:Int, upperBound:Int, modulo:Int):Int = {
    val primesInRange =  (lowerBound to upperBound).filter(isPrime)
  	val modulos = primesInRange.map(x => x % modulo)
  	val modFrequency = modulos.groupBy(x=>x).map({case (elem,listElem) => (elem, listElem.size)})
  	val maxOccurrence = modFrequency.values.max
  	val candidates = modFrequency.filter({case (k,v) => v==maxOccurrence})
  	
  	candidates.keys.min
  }                                               //> mostCommonRemainder: (lowerBound: Int, upperBound: Int, modulo: Int)Int
  
  mostCommonRemainder(1,1000,6)                   //> res1: Int = 5
}