Given an `n x n` 2D matrix, rotate it 90 degrees clockwise in-place (LeetCode 48). Perform layer-by-layer swaps or use transpose+reflect.
2D list of ints.
Modified matrix.
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]]
Example 3:
Input:
matrix = [[1]]
Output:
[[1]]