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Kotlin-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.28

36\. Valid Sudoku

Medium

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.

**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:**

![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png)

**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.

**Constraints:**

*   `board.length == 9`
*   `board[i].length == 9`
*   `board[i][j]` is a digit `1-9` or `'.'`.