48. 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. DO NOT allocate another 2D matrix and do the rotation.
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]]
Constraints:
- n ==
matrix.length
==matrix[i].length
- 1 <= n <= 20
- -1000 <=
matrix[i][j]
<= 1000
画图间距n-1-j
和 i
- 遍历行i的范围为
range(n // 2 + n % 2)
- 遍历列j的范围为
range(n // 2)
class Solution:
def rotate(self, matrix: List[List[int]]) -> None:
"""
Do not return anything, modify matrix in-place instead.
"""
n = len(matrix[0])
for i in range(n // 2 + n % 2):
for j in range(n // 2):
temp = matrix[n-1-j][i]
matrix[n-1-j][i] = matrix[n-1-i][n-1-j]
matrix[n-1-i][n-1-j] = matrix[j][n-1-i]
matrix[j][n-1-i] = matrix[i][j]
matrix[i][j] = temp