public static boolean sim(int[] a, int i) {

        // check if I reached the middle of the array
        if (i == a.length / 2 || i + 1 == a.length) {

            // if array's length is even, need to check the two mid cells
            if (a.length % 2 == 0)
                return a[i] == a[i - 1] ? true : false;

            // if odd, there's only one cell in the middle, So I don't need to check anything.
            return true;

        } else {

            return a[i] == a[a.length - i - 1] ? true && sim(a, i + 1) : false && sim(a, i + 1);
        }

    }

    public static void main(String[] args) {
        int[] a = { 1, 2, 4, 2, 1 };
        System.out.println(sim(a, 0));
    }