Rotate Image leetcode

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

思路是先把matrix按照对角线翻转 再按照垂直翻转 时间 O(n * n)

1 2 3       1 4 7         7 4 1

4 5 6 --> 2 5 8 -- >  8 5 2

7 8 9       3 6 9         9 6 3 

public class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix[0].length;
        int temp;
        for(int i = 0; i < n; i++){
            for(int j = i+1; j < n; j++){
                temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
         
        for(int i = 0; i < n; i++){
            for(int j = 0; j < n/2; j++){
                temp = matrix[i][j];
                matrix[i][j] = matrix[i][n-1-j];
                matrix[i][n-1-j] = temp;
            }
        }
    }
}
public class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length==0 || matrix[0].length==0) {
            return;
        }
        int n = matrix.length;
        for (int i = 0; i < n; i++) {
            for (int j = i; j < n - 1 - i; j++) {
                int tem = matrix[i][j];
                matrix[i][j] = matrix[n - 1 - j][i];
                matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1 - j];
                matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];
                matrix[j][n - 1 - i] = tem;
            }
        }
    }
}