Java

package com.company;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class PrintDiagonalsOfSquareMatrix {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int dimension = Integer.parseInt(reader.readLine());
        int[][] matrix = new int[dimension][dimension];
        for (int rows = 0; rows < matrix.length; rows++) {
            int[] elements = Arrays.stream(reader.readLine().split("\\s+")).mapToInt(Integer::parseInt).toArray();
            for (int cols = 0; cols < matrix[rows].length; cols++) {
               matrix[rows][cols] = elements[cols];
            }
        }
        List<String> firstDiagonal = new ArrayList<>();
        List<String> secondDiagonal = new ArrayList<>();
        int diagonalPosition = 0;
        int secondRowCounter = dimension-1;
        for (int row = 0; row < matrix.length; row++) {
            firstDiagonal.add(matrix[row][diagonalPosition]+"");
            secondDiagonal.add(matrix[secondRowCounter][diagonalPosition]+"");
            diagonalPosition++;
            secondRowCounter--;
        }
            System.out.println(String.join(" ", firstDiagonal));
            System.out.println(String.join(" ", secondDiagonal));
    }
}