# 48. Rotate Image

#### Medium

***

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**](https://en.wikipedia.org/wiki/In-place_algorithm), which means you have to modify the input 2D matrix directly. **DO NOT** allocate another 2D matrix and do the rotation.

 

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/08/28/mat1.jpg)

<pre><code>Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
<strong>Output:
</strong> [[7,4,1],[8,5,2],[9,6,3]]
</code></pre>

**Example 2:**

![](https://assets.leetcode.com/uploads/2020/08/28/mat2.jpg)

<pre><code>Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
<strong>Output:
</strong> [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
</code></pre>

&#x20;

**Constraints:**

* `n == matrix.length == matrix[i].length`
* `1 <= n <= 20`
* `-1000 <= matrix[i][j] <= 1000`

```python
class Solution:
    def rotate(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        # Reverse
        left , right = 0, len(matrix)-1
        while left < right:
            matrix[left], matrix[right] = matrix[right], matrix[left]
            left += 1
            right -= 1
        # Transpose
        for i in range(len(matrix)):
            for j in range(i):
                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
        
        
```