rotate_matrix rotate 90 degrees clockwise
- c1 ans , O(1) space,
for i in len(matrix)//2is every circle level,for j in range(i, len(matrix)-1-i)e.g. n=4, outside round and inside round, so 2 rounds in total. for each round, first need 3, second need 1. change i and j, then add ~ to the first one. i j, ~j i, ~i ~j, j ~i (i,j) 1 (~j,i) 13 (~i,~j) 16 (j, ~i) 4 = (~j,i) 13 (~i,~j) 16 (j, ~i) 4 (i,j) 1
def rotate_matrix(square_matrix: List[List[int]]) -> None:
matrix_size = len(square_matrix) - 1
for i in range(len(square_matrix) // 2):
# print(i)
for j in range(i, matrix_size - i):
# Perform a 4-way exchange. Note that A[~i] for i in [0, len(A) - 1]
# is A[-(i + 1)].
(square_matrix[i][j], square_matrix[~j][i], square_matrix[~i][~j],
square_matrix[j][~i]) = (square_matrix[~j][i],
square_matrix[~i][~j],
square_matrix[j][~i],
square_matrix[i][j])
- c2 own brute force
def rotate_matrix(square_matrix: List[List[int]]) -> None:
width = len(square_matrix)
new_square = []
for i in range(width):
last_row = square_matrix.pop(-1)
for j, e in enumerate(last_row):
if len(new_square) < width:
new_square.append([e])
else:
new_square[j].append(e)
square_matrix[:] = new_square
- c0 transpose then exchange row 1,4 2,3
def rotate_matrix(square_matrix):
if not square_matrix:
return []
trans = [[row[i] for row in square_matrix] for i in range(len(square_matrix[0]))]
for i in trans:
for j in range(len(trans[0]) // 2):
i[j], i[len(trans[0]) - 1 - j] = i[len(trans[0]) - 1 - j], i[j]
square_matrix[:] = trans