public static int diagonalDifference(List<List<Integer>> arr) {

        int leftSum = 0;
        int rightSum = 0;
        
        for(int i=0; i<arr.size();i++){
            List<Integer> row = arr.get(i);
            leftSum = leftSum + row.get(i);
            rightSum = rightSum + row.get(row.size() -1  - i);
        }
        
        return leftSum > rightSum ? (leftSum - rightSum) : (rightSum - leftSum);
    }