projecteuler_problem

P5.scala

import scala.collection.mutable.ListBuffer
import scala.collection.mutable.HashMap
import scala.annotation.tailrec
/*
** author fairjm 
** https://projecteuler.net/problem=5
*/
object P5 {
  
  def getPrimesLEQ(num:Int):List[Int] = {
    val buffer = ListBuffer.empty[Int]
    for( i <- 2 to num ){
      if((2 until i).toList.forall(i % _ != 0))  buffer += i
    }
    buffer.toList
  }
  
  def allFactors(num:Int)(implicit fac:List[Int]):Map[Int,Int] = {
    @tailrec
    def factors(last:Int,fs:List[Int],allFs:List[Int]):List[Int] = {
      if(last == 1) fs
      else {
        allFs match {
          case Nil => fs
          case head::tail if last % head == 0 =>
            factors(last / head,head::fs,allFs)
          case head::tail =>
            factors(last,fs,tail)
        }
      }
    }
    factors(num,List.empty[Int],fac).groupBy(num => num).mapValues(_.size)
  }
  
  def main(args: Array[String]): Unit = {
    implicit val primes = getPrimesLEQ(10)
	val map = new HashMap[Int,Int]
	for(i <- 1 to 10 ){
	  allFactors(i).map( t => if(map.getOrElse(t._1, 0) < t._2) map.update(t._1, t._2))
	}
    println(map) // Map(2 -> 3, 5 -> 1, 7 -> 1, 3 -> 2)
  }
}