```
class Solution:
# @param matrix, a list of lists of integers
# @return nothing (void), do not return anything, modify matrix in-place instead.
def rotate(self, matrix):
if matrix is None:
return
m = len(matrix)
for i in range(m):
for j in range(i,m-i-1):
row = j
col = m-1-i
while not (row == i and col == j):
mid = matrix[row][col]
matrix[row][col] = matrix[i][j]
matrix[i][j] = mid
row1 = row
col1 = col
row = col1
col = m-1-row1
```