36. Valid Sudoku

class Solution:
    def isValidSudoku(self, board):
        """
        :type board: List[List[str]]
        :rtype: bool
        """
        row = {}
        for i in range(9):
            row[i] = set()

        colos = {}
        for i in range(9):
            colos[i] = set()

        squares = {}
        for i in range(3):
            squares[i] = {}
            for j in range(3):
                squares[i][j] = set()

        for i in range (len(board)):
            for j in range(len(board[0])):
                num = board[i][j]
                if num != '.':
                    if num in row[i]:
                        return False
                    else:
                        row[i].add(num)

                    if num in colos[j]:
                        return False
                    else:
                        colos[j].add(num)

                    if num in squares[i//3][j//3]:
                        return False
                    else:
                        squares[i//3][j//3].add(num)
        return True