public class DayCode {    public static void main(String[] args) {        int[][] matrix = new int[][]{{1, 2}, {3, 4}};        List<Integer> ans = new DayCode().spiralOrder(matrix);        System.out.println(ans.toString());    }
    /**     * 时间复杂度O(rows * cols)     * 空间复杂度O(rows * cols)     * https://leetcode-cn.com/problems/spiral-matrix/     *     * @param matrix     * @return     */    public List<Integer> spiralOrder(int[][] matrix) {        List<Integer> ans = new ArrayList<>();        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {            return ans;        }
        int rows = matrix.length;        int cols = matrix[0].length;        int total = rows * cols;        boolean[][] visited = new boolean[rows][cols];        int row = 0;        int col = 0;        int[][] directions = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};        int directionIdx = 0;        for (int i = 0; i < total; i++) {            ans.add(matrix[row][col]);            visited[row][col] = true;            int nextRow = row + directions[directionIdx][0];            int nextCol = col + directions[directionIdx][1];            if (nextRow < 0 || nextRow >= rows || nextCol < 0 || nextCol >= cols || visited[nextRow][nextCol]) {                directionIdx = (directionIdx + 1) % 4;            }            row += directions[directionIdx][0];            col += directions[directionIdx][1];        }        return ans;    }}