# 36. Valid Sudoku

### On This Page

Determine if a `9 x 9`

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 nine 3 x 3 sub-boxes of the grid must contain the digits `1-9`

without repetition.

**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.

**Example 1:**

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

**Example 2:**

```
Input: 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"]]
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.
```

## Code

**Idea:**

```
class Solution:
def isValidSudoku(self, board: List[List[str]]) -> bool:
exist = set()
for i in range(9):
for j in range(9):
x = board[i][j]
if x != '.':
uniqs = (
(i, x),
(x, j),
(int(i/3), int(j/3), x) ) # devide 3 because of third check in 3x3 block
for z in uniqs:
if z in exist:
return False
exist.add(z)
return True
```