LC048 - Rotate Image

Problem

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

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]

Output: [[7,4,1],[8,5,2],[9,6,3]]

Solution

Time complexity is $O(n\cdot n)$ and no extra space is used.

def rotate(self, matrix: List[List[int]]) -> None:
	for i in range(len(matrix)+1):
		for j in range(i, len(matrix[0])):
			matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]

	for row in range(len(matrix)):
		matrix[row] = matrix[row][::-1]