https://leetcode.com/problems/rotate-image/
You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly.
DO NOT allocate another 2D matrix and do the rotation.
Example 1:
Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]
Example 2:
Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
ps: 实际上这是图片处理非常有用的一种算法，常见的图片旋转就是这么实现的。
Constraints:
matrix.length == n matrix[i].length == n 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000