public static void main(String[] args) {
        int[] A = {3,5,6,3,3,5};
        int[] B = {-1000000000,3,5,6,-1000000000};
        int[] C = new int[0];

        System.out.println(solution(A));
        System.out.println(solution(B));
        System.out.println(solution(C));
    }

    private static int solution(int[] A){
        int counter = 0;
        if(A.length == 1){
            return 0;
        }
        for( int index = 0; index < A.length; index++) {
            int currentToCheck = A[index];

            for (int j = 1; j < A.length; j++) {
                if (index < j && currentToCheck == A[j]) {
                    counter++;
                }
            }
        }
        return counter;
    }