Task: Sequence C contains elements from A if they are present in B p times, and p is prime number

KotlinExcercise.kt

import kotlin.math.*

fun main() {
    val a = arrayListOf(2, 3, 9, 2, 5, 1, 3, 7, 10)
    val b = intArrayOf(2, 1, 3, 4, 3, 10, 6, 6, 1, 7, 10, 10, 10)
    val c = ArrayList<Int>(a)
    for(i in b){
    	if(isPrimeNumber(countNumber(i, b)))
        //if we didn't care about original contents of A, at this point we could remove the values from A and we would get the expected C.
        	c.remove(i)
    }
    //And just to prove that it works, we print it all out
    for(i in c)
		println(i)
}

//Primality test
fun isPrimeNumber(n : Int) : Boolean {
  if (n < 2)
    return false
  val upperRange = floor(sqrt(n.toDouble())).toInt()
  for(i in 2..upperRange){
	val division = n%i
   if(division == 0)
		return false
  }
  return true
}

fun countNumber(n : Int, sequence : IntArray) : Int{
    val predicate : (Int) -> Boolean = { it == n}
    return sequence.count(predicate)    
}