36

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:

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 or '.'.

Companies:
DoorDash, Microsoft, Amazon, Apple, Oracle, Uber, Goldman Sachs, Wayfair

Related Topics:
Array, Hash Table, Matrix

Similar Questions:

• Sudoku Solver (Hard)

Solution 1.

// OJ: https://leetcode.com/problems/valid-sudoku/
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& A) {
        int row[9][9] = {}, col[9][9] = {}, box[9][9] = {};
        for (int i = 0; i < 9; ++i) {
            for (int j = 0; j < 9; ++j) {
                if (A[i][j] == '.') continue;
                int n = A[i][j] - '1';
                if (row[i][n] || col[j][n] || box[i / 3 * 3 + j / 3][n]) return false;
                row[i][n] = col[j][n] = box[i / 3 * 3 + j / 3][n] = 1;
            }
        }
        return true;
    }
};