class Solution:

def isValidSudoku(self, board):

"""

:type board: List[List[str]]

:rtype: bool

"""

if not board or not board[0] or len(board) != len(board[0]):

return False

n = len(board)

EMPTY = '.'

CANDS = '123456789'

for x in range(n):

used = set()

for y in range(n):

if board[x][y] == EMPTY:

continue

if board[x][y] not in CANDS:

return False

if board[x][y] in used:

return False

used.add(board[x][y])

for y in range(n):

used = set()

for x in range(n):

if board[x][y] == EMPTY:

continue

if board[x][y] in used:

return False

used.add(board[x][y])

for i in range(3):

for j in range(3):

used = set()

for x in range(i * 3, i * 3 + 3):

for y in range(j * 3, j * 3 + 3):

if board[x][y] == EMPTY:

continue

if board[x][y] in used:

return False

used.add(board[x][y])

return True