判斷乙個 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。
上圖是乙個部分填充的有效的數獨。
數獨部分空格內已填入了數字，空白格用 『.』 表示。
示例1：
輸入：
[ ["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"]
] 輸出：true
輸入：
[ ["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"]
] 輸出：false
解釋：除了第一行的第乙個數字從 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。
廢話少說，直接上**：
class solution:
def isvalidsudoku(self, board):
""":type board: list[list[str]]
:rtype: bool
"""r, c, g= [''] * 9, [''] * 9, [''] * 9
for r, array in enumerate(board):
for c, str in enumerate(array):
g = r // 3 * 3 + c // 3
if str != '.':
if (str in r[r]) or (str in c[c]) or (str in g[g]):
return false
r[r] += str
c[c] += str
g[g] += str
return true
這個問題，先把大問題分成幾個小問題，拿到面板上的任何乙個元素，判斷它所在行（列）是否有相同元素，以及它所在的粗實線分割的9宮格中是否有相同元素。
好了，我相信，重點就在9宮格如何定位。
實際上外層迴圈的前三次和內層迴圈的前三次表示的是索引為0也就是第乙個九宮格，外層迴圈的前三次和內層迴圈的中間三次表示的是索引為1也就是第二個九宮格，外層迴圈的前三次和內層迴圈的後三次表示的是索引為2也就是第三個九宮格。。。以此類推，於是我們找出了這麼乙個關係：九宮格的索引g = r // 3 * 3 + c // 3。
這就是9宮格的定位。
然後是關於如何判斷數字是否存在重複，這裡使用字串拼接的方式將每行（列）以及每乙個9宮格中出現的有效字元（』.'除外）拼接在一起，實際上r/c/g這三個陣列中儲存的元素本質上是相同的，只不過它們分別是按行（列）以及9宮格來統計的。
希望讀到這裡，各位能有所感悟。
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