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.
Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]
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]]
Input: matrix = [[1]]
Output: [[1]]
Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]
matrix.length == n
matrix[i].length == n
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000
Solutions (Click to expand)
Rotating a matrix by 90 degrees requires us to turn all the columns into rows and vice versa. We can do this by transposing the matrix.
This involves swapping cells with their reflection along the diagonal axis
In doing so, we've essentially created a reversed version of a rotated matrix. We can reverse it again by reflecting it along the y axis
This involves swapping cells with their reflection along the y axis
Time: O(N) Where N is the total number of cells in the matrix
Space: O(1)