DiagonalDifference.java

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

public class DiagonalDifference {

    public static int diagonalDifference(List<List<Integer>> arr) {
        int d1 = 0, d2 = 0;
        int n = arr.size();

        for (int i = 0; i < n; i++) {
            d1 += arr.get(i).get(i);
        }

        for (int i = 0; i < n; i++) {
            d2 += arr.get(i).get(n - i - 1);
        }
        return Math.abs(d1 - d2);
    }

    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int n = Integer.parseInt(bufferedReader.readLine().trim());

        List<List<Integer>> arr = new ArrayList<>();

        IntStream.range(0, n).forEach(i -> {
            try {
                arr.add(
                        Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                                .map(Integer::parseInt)
                                .collect(toList())
                );
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        });

        int result = diagonalDifference(arr);

        bufferedWriter.write(String.valueOf(result));
        bufferedWriter.newLine();

        bufferedReader.close();
        bufferedWriter.close();
    }
}