簡單來說就是為給一個二維陣列，請確定給的二維陣列是合法的數獨矩陣。

範例：

分段檢查

class Solution:
    def isValidSudoku(self, board: List[List[str]]) -> bool:

        # row  validation 
        for row in board:
            seen = dict()
            for i in row:
                if i == ".":
                    continue
                if i not in seen:
                    seen[i] = True
                else:
                    return False 

        # column validation 
        for col in range(len(board)):
            seen = dict()
            for row in range(len(board)):
                if board[row][col] == ".":
                    continue

                if board[row][col] not in seen:
                    seen[board[row][col]] = True
                else:
                    return False 


        # box validations 
        for group in [(0,1,2),(3,4,5),(6,7,8)]:
            d1 = {} 
            d2 = {} 
            d3 = {}
            for row in group:
                for col in range(len(board)):
                    key = board[row][col]  
                    if key == ".":
                        continue
                    if col < 3:
                        if key not in d1:
                            d1[key] = True
                        else:
                            return False 
                    elif col < 6:
                        if key not in d2:
                            d2[key] = True
                        else:
                            return False 
                    else:
                        if key not in d3:
                            d3[key] = True
                        else:
                            return False 

        return True 

這個方法，我們分成三個部分來檢查是否是合法的數獨：

橫的檢查

# row  validation 
for row in board:
    seen = dict()
    for i in row:
        if i == ".":
            continue
        if i not in seen:
            seen[i] = True
        else:
            return False 

直的檢查

# column validation 
for col in range(len(board)):
    seen = dict()
    for row in range(len(board)):
        if board[row][col] == ".":
            continue

        if board[row][col] not in seen:
            seen[board[row][col]] = True
        else:
            return False 

箱型檢查

最後這個比較難，箱型檢查。概念主要是，先由上而下，每三個分成一組，最後再將每組切成三個部分進行檢查。

# box validations 
for group in [(0,1,2),(3,4,5),(6,7,8)]:
    d1 = {} 
    d2 = {} 
    d3 = {}
    for row in group:
        for col in range(len(board)):
            key = board[row][col]  
            if key == ".":
                continue
            if col < 3:
                if key not in d1:
                    d1[key] = True
                else:
                    return False 
            elif col < 6:
                if key not in d2:
                    d2[key] = True
                else:
                    return False 
            else:
                if key not in d3:
                    d3[key] = True
                else:
                    return False 

如果覺得分段程式碼太長，這邊提供組合起來的。