solution1.java

import java.util.*;

public class Solution {

    private static boolean isPrime(int n) {
        if (n < 2) return false;
        for (int i = 2; i * i <= n; i++)
            if (n % i == 0 || n % (n - i) == 0)
                return false;
        return true;
    }

    private static List<Integer> filterPrimeTimesOccurences(List<Integer> a, List<Integer> b) {
        HashMap<Integer, Integer> countingInB = new HashMap<>();
        // Store occurences number for each number in B.
        for (int value : b) {
            countingInB.putIfAbsent(value, 0);
            int count = countingInB.getOrDefault(value, 0);
            countingInB.put(value, count + 1);
        }
        // Filter a.
        List<Integer> filteredA = new ArrayList<>();
        for (int value : a) {
            if (!isPrime(countingInB.getOrDefault(value, 0)))
                filteredA.add(value);
        }
        return filteredA;
    }

    public static void main(String[] args) {
        Integer[] A = new Integer[] {2,3,9,2,5,1,3,7,10};
        List<Integer> a =  new ArrayList<>(Arrays.asList(A));

        Integer[] B = new Integer[] {2,1,3,4,3,10,6,6,1,7,10,10,10};
        List<Integer> b =  new ArrayList<>(Arrays.asList(B));

        filterPrimeTimesOccurences(a, b).forEach(System.out::println);

    }
}