public static int diagonalDifference(List<List<Integer>> arr) {
        int leftsum = 0, rightsum = 0;
        for(int i = 0; i < arr.size(); i++){
            leftsum += arr.get(i).get(i);
            rightsum += arr.get(arr.size() - (i + 1) ).get(i);
        }

        return Math.max(rightsum, leftsum) - Math.min(rightsum, leftsum);
    }