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Valid Sudoku⚓︎

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Description⚓︎

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:

sudoku

  • Input:
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 2
 3
 4
 5
 6
 7
 8
 9
10
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:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
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 '.'.

Solution⚓︎

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class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        int row[9][9];
        int col[9][9];
        int box[3][3][9];
        memset(row, 0, sizeof(row));
        memset(col, 0, sizeof(col));
        memset(box, 0, sizeof(box));
        for (int i = 0; i < board.size(); i++) {
            for (int j = 0; j < board[0].size(); j++) {
                if (board[i][j] == '.') continue;
                int num = board[i][j] - '1';
                if (row[i][num] || col[j][num] || box[i / 3][j / 3][num])
                    return false;
                row[i][num] = col[j][num] = box[i / 3][j / 3][num] = 1;
            }
        }
        return true;
    }
};