Lucky Numbers in a Matrix

/*
 * Problem : Process a matrix.
 * Input   : r and c, then r rows of c integers.
 * Output  : The lucky numbers.
 * Approach: Row minimums and column maximums.
 * Time    : O(r * c)
 * Space   : O(r + c)
 * 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 rows = m.length;
        int cols = m[0].length;

        // Step 1: Find the smallest value of every row and the biggest value of every column.
        int[] rowMin = new int[rows];
        int[] colMax = new int[cols];
        java.util.Arrays.fill(rowMin, Integer.MAX_VALUE);
        java.util.Arrays.fill(colMax, Integer.MIN_VALUE);
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                rowMin[i] = Math.min(rowMin[i], m[i][j]);
                colMax[j] = Math.max(colMax[j], m[i][j]);
            }
        }

        // Step 2: A lucky number equals both its row minimum and its column maximum. TreeSet sorts and removes repeated values.
        java.util.TreeSet<Integer> lucky = new java.util.TreeSet<>();
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                if (m[i][j] == rowMin[i] && m[i][j] == colMax[j]) {
                    lucky.add(m[i][j]);
                }
            }
        }

        // Step 3: Make the output text.
        if (lucky.isEmpty()) {
            return "none";
        }
        StringBuilder text = new StringBuilder();
        for (int value : lucky) {
            text.append(text.length() == 0 ? "" : " ").append(value);
        }
        return text.toString();
    }

    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));
    }
}