Project euler problem 3 solution

Issue3.scala

import java.lang.Math

object Issue3 {
  def isPrime(n: Long) = {
    if (n <= 1) false
    else if (n == 2) true
    else if (n % 2 == 0) false
    else {
      val max = Math.sqrt(n).toInt
      !3.to(max, 2).exists(n % _ == 0)
    }
  }

  def maxFactorOf(n: Long): Long = {
    val max = Math.sqrt(n).toInt
    val factor = max.to(2, -1).collectFirst {case i: Int if n % i == 0 && isPrime(i) => i}

    if (factor == None) n else factor.get
  }

  def main(args: Array[String]) {
    assert(6857 == maxFactorOf(600851475143L))
  }
}