> For the complete documentation index, see [llms.txt](https://joshualbarb.gitbook.io/leetcode-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://joshualbarb.gitbook.io/leetcode-problems/hash-table/valid-sudoku.md).

# Valid Sudoku

## Problem

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

1. Each row must contain the digits `1-9` without repetition.
2. Each column must contain the digits `1-9` without repetition.
3. Each of the nine `3 x 3` sub-boxes of the grid must contain the digits `1-9` without repetition.

## Solution

```
class Solution:
    def isValidSudoku(self, board: List[List[str]]) -> bool:
        row = set()
        column = set()
        block = set()
        
        for i in range(len(board)):
            for j in range(len(board[0])):
                if board[i][j] != ".":   
                    r = (i,board[i][j])
                    c = (j, board[i][j])
                    b = (i//3,j//3, board[i][j])
                
                    if r in row or c in column or b in block:
                        return False
                
                    row.add(r)
                    column.add(c)
                    block.add(b)
        
        return True
        
#We need to keep track of the digits we see in each row,
#column, and block

#We will have 3 hash sets (row, column, block), storing the
#number along with the row/column/block we saw the 
#number in. Whenever we encounter a digit already seen,
#we know the sudoku is not valid.

#Time: O(n^2)
#Space: O(n) for the sets
```