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.
Constraints:
- n == matrix.length == matrix[i].length
- 1 <= n <= 20
- -1000 <= matrix[i][j] <= 1000
Examples:
Input: [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]
Explanation: The image is rotated by 90 degrees clockwise.
Solutions
Transpose and Reverse
Time: O(n^2)Space: O(1)
The solution first transposes the matrix (i.e., swaps the row and column indices of each element), and then reverses each row to achieve the rotation effect.
def rotate(matrix):
n = len(matrix); for i in range(n):
for j in range(i, n):
matrix[j][i], matrix[i][j] = matrix[i][j], matrix[j][i]; for i in range(n):
matrix[i] = matrix[i][::-1]Follow-up:
How would you rotate the image by 180 degrees or 270 degrees?
