public class DayCode {    public static void main(String[] args) {        int n = 3;        int[][] ans = new DayCode().generateMatrix(n);        System.out.println(Arrays.deepToString(ans));    }
    /**     * 题目链接: https://leetcode-cn.com/problems/spiral-matrix-ii/     * 时间复杂度 O(n)     * 空间复杂度 O(n * n)     *     * @param n     * @return     */    public int[][] generateMatrix(int n) {        int[][] ans = new int[n][n];        boolean[][] visited = new boolean[n][n];        int[][] directions = new int[][]{{0, 1}, {1, 0}, {0, -1}, {-1, 0}};        int directionIdx = 0;        int row = 0;        int col = 0;        for (int i = 1; i <= n * n; i++) {            ans[row][col] = i;            visited[row][col] = true;            int nextRow = row + directions[directionIdx][0];            int nextCol = col + directions[directionIdx][1];            if (nextRow < 0 || nextRow >= n || nextCol < 0 || nextCol >= n || visited[nextRow][nextCol]) {                directionIdx = (directionIdx + 1) % 4;            }            row += directions[directionIdx][0];            col += directions[directionIdx][1];        }
        return ans;    }}