Software Mansion task

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;

public class Main {

    public static void main(String[] args) {
        Integer[] A = {2,3,9,2,5,1,3,7,10};
        Integer[] B = {2,1,3,4,3,10,6,6,1,7,10,10,10};

        System.out.println(useTheAlgorithm(A, B));
    }

    private static ArrayList<Integer> useTheAlgorithm(Integer[] listA, Integer[] listB){
        HashMap<Integer, Integer> listBWithCounters = new HashMap<>();

        for(Integer elementB : listB){
            listBWithCounters.compute(elementB, (key, val) -> (val == null) ? 1 : val + 1);
        }

        ArrayList<Integer> resultList = new ArrayList<>(Arrays.asList(listA));

        for(Integer elementA : listA){
            Integer counter = listBWithCounters.get(elementA);

            if(counter != null && isPrime(counter)){
                resultList.remove(elementA);
            }
        }

        return resultList;
    }

    private static boolean isPrime(int num){
        if(num <= 3) return num > 1;
        if(num % 2 == 0) return false;

        int i = 5;
        while(Math.pow(i, 2) <= num){
            if(num % i == 0) return false;
            i += 2;
        }
        return true;
    }
}