IntStreamTask.java

public static int diagonalDifference(int size, List<List<Integer>> arr) {
        int sum1, sum2;

        sum1 = IntStream
                .range(0, size)
                .map(i -> arr.get(i).get(i))
                .sum();

        sum2 = IntStream
                .range(0, size)
                .map(i -> arr.get(i).get((size - 1) - i))
                .sum();

        return Math.abs(sum1 - sum2);
    }