public static int diagonalDifference(List<List<Integer>> arr) {
        // Write your code here
        int           sumLeftToRight = 0;
        int           sumRightToLeft = 0;
        int           n              = arr.size();

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (i == j) {
                    sumLeftToRight += arr.get(i).get(j);
                }
                if (i + j ==  (n - 1)) {
                    sumRightToLeft += arr.get(i).get(j);
                }
            }
        }
        return Math.abs(sumLeftToRight - sumRightToLeft);
    }