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]]

**Constraints:**

`n == matrix.length == matrix[i].length`

`1 <= n <= 20`

`-1000 <= matrix[i][j] <= 1000`

Solution:

Time complexity: **O(N)**, each index value in matrix is read and written once.

Space complexity: **O(1)**, no matrix variable is being declared or created, but used matrix recursively.