判断一个 9x9 的数独是否有效。只需要根据以下规则，验证已经填入的数字是否有效即可。
数字 1-9 在每一行只能出现一次。数字 1-9 在每一列只能出现一次。数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。上图是一个部分填充的有效的数独。
数独部分空格内已填入了数字，空白格用 '.' 表示。
示例 1:
输入: [ ["5","3",".",".","7",".",".",".","."], ["6",".",".","1","9","5",".",".","."], [".","9","8",".",".",".",".","6","."], ["8",".",".",".","6",".",".",".","3"], ["4",".",".","8",".","3",".",".","1"], ["7",".",".",".","2",".",".",".","6"], [".","6",".",".",".",".","2","8","."], [".",".",".","4","1","9",".",".","5"], [".",".",".",".","8",".",".","7","9"] ] 输出: true示例 2:
输入: [ ["8","3",".",".","7",".",".",".","."], ["6",".",".","1","9","5",".",".","."], [".","9","8",".",".",".",".","6","."], ["8",".",".",".","6",".",".",".","3"], ["4",".",".","8",".","3",".",".","1"], ["7",".",".",".","2",".",".",".","6"], [".","6",".",".",".",".","2","8","."], [".",".",".","4","1","9",".",".","5"], [".",".",".",".","8",".",".","7","9"] ] 输出: false 解释: 除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。 但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。说明:
一个有效的数独（部分已被填充）不一定是可解的。只需要根据以上规则，验证已经填入的数字是否有效即可。给定数独序列只包含数字 1-9 和字符 '.' 。给定数独永远是 9x9 形式的。解题思路：使用三个字典列表来分别存储行，列，3x3单元区域的数字，若当前数字已存在，则返回Fasle，否则，将数字添加到行，列，区域字典列表中对应的字典中去。
Python3代码如下：
class Solution(object): def isValidSudoku(self, board): """ :type board: List[List[str]] :rtype: bool """ row = [{},{},{},{},{},{},{},{},{}] col = [{},{},{},{},{},{},{},{},{}] area = [{},{},{},{},{},{},{},{},{}] for i in range(9): for j in range(9): area_index = (i//3)*3+(j//3) if board[i][j] != '.': if board[i][j] not in row[i] and board[i][j] not in col[j] and board[i][j] not in area[area_index]: row[i][board[i][j]] = 1 col[j][board[i][j]] = 1 area[area_index][board[i][j]] = 1 else: return False return True