not confusing at all solution

package com.codeit08_04;

import java.io.*;

public class B_Diagonals {
    public static void main(String[] args) throws IOException {
        File file = new File("diagonalsum.in");
        FileReader fr = new FileReader(file);
        BufferedReader reader = new BufferedReader(fr);

        int matrixSize = Integer.parseInt(reader.readLine());
        int[][] matrix = new int[matrixSize][matrixSize];
        for (int i = 0; i < matrixSize; i++) {
            matrix[i] = intParse(reader.readLine().split(" "));
        }


        int[] rightDiag = new int[matrixSize * 2 - 1];
        int[] leftDiag = new int[matrixSize * 2 - 1];

        for (int r = 0, c = 0; c < matrixSize; c++) {
            int sum = 0;
            for (int row = r, col = c; col < matrixSize; row++, col++) {
                sum += matrix[row][col];
            }
            rightDiag[matrixSize - 1 + c] = sum;
        }

        for (int r = 1, c = 0; r < matrixSize; r++) {
            int sum = 0;
            for (int row = r, col = c; row < matrixSize; row++, col++) {
                sum += matrix[row][col];
            }
            rightDiag[matrixSize - 1 - r] = sum;
        }

        for (int r = 0, c = matrixSize - 1; c >= 0; c--) {
            int sum = 0;
            for (int row = r, col = c; col >= 0; row++, col--) {
                sum += matrix[row][col];
            }
            leftDiag[matrixSize - 1 - (matrixSize - 1 - c)] = sum;
        }

        for (int r = 1, c = matrixSize - 1; r < matrixSize; r++) {
            int sum = 0;
            for (int row = r, col = c; row < matrixSize; row++, col--) {
                sum += matrix[row][col];
            }
            leftDiag[matrixSize - 1 + r] = sum;
        }

        int count = Integer.parseInt(reader.readLine());
        StringBuilder output = new StringBuilder();

        for (int i = 0; i < count; i++) {
            int[] pos = intParse(reader.readLine().split(" "));
            pos[0]--;
            pos[1]--;
            int rightPos = matrixSize - 1 - (pos[0] - pos[1]);
            int right = rightDiag[rightPos];
            int leftPos = pos[1] + pos[0];
            int left = leftDiag[leftPos];
            int element = matrix[pos[0]][pos[1]];

            int result = right + left - element;

            output.append(result).append(System.lineSeparator());
        }

        try (
                OutputStream outputStream = new FileOutputStream("diagonalsum.out");
                BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream))
        ) {
            bufferedWriter.write(output.toString());
            bufferedWriter.flush();
        }
    }

    private static int[] intParse(String[] elements) {
        int[] ints = new int[elements.length];
        for (int i = 0; i < elements.length; i++) {
            ints[i] = Integer.parseInt(elements[i]);
        }

        return ints;
    }
}