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.*

//Task: Sequence C contains elements from A if they are present in B p times, and p is prime number
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)
        
  //check every unique number in B sequence
  for(i in b.distinct()){
    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.
    // while loop to remove all of the instances of checked number.
      while(c.contains(i))
        c.remove(i)
  }
    
  //And just to prove that it works, we print it all out
  for(i in c)
    println(i)
}

//Naive primality test
//This works well for small set of data, with the complexity of O(n).
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)    
}