# 25. \[matrix] Valid Sudoku

**36. Valid Sudoku**

**Medium**

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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 the5 in the top left corner being modified to8. 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 `'.'`.

{% embed url="<https://leetcode.com/problems/valid-sudoku/>" %}

> Time: O(1)

> Space: O(1)

```jsx
/**
 * @param {character[][]} board
 * @return {boolean}
 */
const points = [
    [0, 0],
    [0, 3],
    [0, 6],
    [3, 0],
    [3, 3],
    [3, 6],
    [6, 0],
    [6, 3],
    [6, 6],
];

const set = new Set();

var isValidSudoku = function(board) {
    let flag = true;

    for (let i = 0; i < 9; i++) {
        set.clear();
        flag = checkRow(i, board);
        if (!flag) return false;
        
        set.clear();
        flag = checkColumn(i, board);
        if (!flag) return false;
    }

    for (const [row, col] of points) {
        set.clear();
        flag = check(row, col, board);
        if (!flag) return false;
    }

    return flag;
};

function checkRow(col, board) {
    for (let i = 0; i < 9; i++) {
        const curr = board[i][col];
        if (curr === '.') 
            continue;
        if (set.has(curr)) 
            return false;
        set.add(curr);
    }
    return true;
}

function checkColumn(row, board) {
    for (let i = 0; i < 9; i++) {
        const curr = board[row][i];
        if (curr === '.') 
            continue;
        if (set.has(curr)) 
            return false;
        set.add(curr);
    }
    return true;
}

function check(row, col, board) {
    for (let i = 0; i < 3; i++) {
        for (let j = 0; j < 3; j++) {
            const curr = board[row + i][col + j];
            if (curr === '.') 
                continue;
            if (set.has(curr))
                return false;

            set.add(curr);
        }
    }
    return true;
}
```


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