Euler Problem3

euler_p3.scala

@tailrec
  def getMinFactor(num: Long, divisor: Long = 2L): Long = {
    if(divisor > Math.sqrt(num)) num
    else if(num % divisor == 0) divisor
    else getMinFactor(num, divisor+1)
  }                                               //> smallestFactor: (num: Long, divisor: Long)Long

  def getMaxPrimeFactor(num: Long): Long = {
    @tailrec
    def run(num: Long, minFactor: Long): Long = {
      val next = num / minFactor
      if(next <= 1) num else run(next, getMinFactor(next))
    }

    run(num, getMinFactor(num))
  }                                               //> greatestFactor: (num: Long, prime: Long)Long
  
  getMaxPrimeFactor(600851475143L)                //> 6857