# Question

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

- Each row must contain the digits 1-9 without repetition.
- Each column must contain the digits 1-9 without repetition.
- Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

The Sudoku board could be partially filled, where empty cells are filled with the character ‘.’.

Example 1:

```
Input:
[
["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"]
]
Output: true
```

Example 2:

```
Input:
[
["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"]
]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being
modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
```

Note:

- A Sudoku board (partially filled) could be valid but is not necessarily solvable.
- Only the filled cells need to be validated according to the mentioned rules.
- The given board contain only digits 1-9 and the character ‘.’.
- The given board size is always 9x9.

# Solution

```
class Solution:
def isValidSudoku(self, board):
"""
:type board: List[List[str]]
:rtype: bool
"""
for l in board:
if self.validate(l) == False:
return False
for i in range(0, 9):
if self.validate([l[i] for l in board]) == False:
return False
for i in range(0, 3):
for j in range(0, 3):
l = list()
for k in range(0, 3):
l.extend(board[j * 3 + k][i*3:(i+1)*3])
if self.validate(l) == False:
return False
return True
def validate(self, block):
num_set = set()
for n in block:
if n != ".":
num = int(n)
if 1 <= num <= 9 and num not in num_set:
num_set.add(num)
else:
return False
return True
```