rotate_image.py

"""
You are given an n x n 2D mat representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?
"""


# clockwise rotate
# first reverse up to down, then swap the symmetry
# 1 2 3 7 8 9 7 4 1
# 4 5 6 => 4 5 6 => 8 5 2
# 7 8 9 1 2 3 9 6 3

defrotate(mat):
ifnotmat:
returnmat
mat.reverse()
foriinrange(len(mat)):
forjinrange(i):
mat[i][j], mat[j][i] =mat[j][i], mat[i][j]
returnmat


if__name__=="__main__":
mat= [[1, 2, 3],
 [4, 5, 6],
 [7, 8, 9]]
print(mat)
rotate(mat)
print(mat)