Sum of the Diagonals of a Square Matrix

/*
 * Problem : Process a matrix.
 * Input   : r and c, then r rows of c integers.
 * Output  : Two sums.
 * Approach: One loop is enough.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String solve(int[][] m) {
        int n = m.length;
        long main = 0;
        long anti = 0;

        for (int i = 0; i < n; i++) {
            // Step 1: The main diagonal has the positions (0,0), (1,1), (2,2), ...
            main += m[i][i];

            // Step 2: The anti-diagonal has the positions (0,n-1), (1,n-2), ...
            anti += m[i][n - 1 - i];
        }

        // Step 3: Print both sums.
        return "main=" + main + " anti=" + anti;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int rows = scanner.nextInt();
        int cols = scanner.nextInt();
        int[][] m = new int[rows][cols];
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                m[i][j] = scanner.nextInt();
            }
        }
        System.out.println(solve(m));
    }
}