請你判斷一個9x9 的數獨是否有效。只需要 根據以下規則 ，驗證已經填入的數字是否有效即可。

數字1-9在每一行只能出現一次。
數字1-9在每一列只能出現一次。
數字1-9在每一個以粗實線分隔的3x3宮內只能出現一次。（請參考示例圖）
數獨部分空格內已填入了數字，空白格用'.'表示。

注意：

一個有效的數獨（部分已被填充）不一定是可解的。
只需要根據以上規則，驗證已經填入的數字是否有效即可。

示例 1：

輸入：board =
[["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"]]
輸出：true
示例 2：

輸入：board =
[["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"]]
輸出：false
解釋：除了第一行的第一個數字從 5 改為 8 以外，空格內其他數字均與 示例1 相同。 但由於位於左上角的 3x3 宮內有兩個 8 存在, 因此這個數獨是無效的。

提示：

board.length == 9
board[i].length == 9
board[i][j] 是一位數字或者 '.'

常規寫法(行, 列, 小數獨遍歷判斷是否重複)

from collections import defaultdict
class Solution:
    def isValidSudoku(self, board) -> bool:
        # 數獨
        rows, cols = defaultdict(set), defaultdict(set) # 行, 列
        c = defaultdict(set) # 小數獨

        # 計數大於1, 則返回false
        
 
for i in range(9):
            for j in range(9):
                if board[i][j] == '.':
                    continue # 無需判斷

                # 小數獨
                c_index = i // 3 * 3 + j // 3 # 上面i佔的小數獨數量 + 下面j佔的小數獨數量 

                # rows[0], rows[1]... rows[8] 判斷是否存在重複數字
                if (board[i][j] in rows[i]) or (board[i][j] in cols[j]) or (board[i][j] in c[c_index]):
                    return False

                rows[i].add(board[i][j])
                cols[j].add(board[i][j])
                c[c_index].add(board[i][j])
            
        return True