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.
Test Cases
Example 1:
| 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 |
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:
| 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 |
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.
Solution
class Solution {
public boolean isValidSudoku(char[][] board) {
boolean[][] col = new boolean[9][9];
boolean[][] row = new boolean[9][9];
boolean[][] block = new boolean[9][9];
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
if (board[i][j] == '.') {
continue;
}
int digit = board[i][j] - '1';
int blockId = i / 3 * 3 + j / 3;
if (row[i][digit]) return false;
if (col[j][digit]) return false;
if (block[blockId][digit]) return false;
row[i][digit] = true;
col[j][digit] = true;
block[blockId][digit] = true;
}
}
return true;
}
}