leetcode.36. 有效的数独

请你判断一个 9 x 9 的数独是否有效。只需要 根据以下规则 ，验证已经填入的数字是否有效即可。

数字 1-9 在每一行只能出现一次。
数字 1-9 在每一列只能出现一次。
数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图）
 

注意：

一个有效的数独（部分已被填充）不一定是可解的。
只需要根据以上规则，验证已经填入的数字是否有效即可。
空白格用 '.' 表示。
 

示例 1：

 

 

输入：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"]]
输出：true
示例 2：

输入：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"]]
输出：false
解释：除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。 但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。
 

提示：

board.length == 9
board[i].length == 9
board[i][j] 是一位数字（1-9）或者 '.'

来源：力扣（LeetCode）
链接：https://leetcode.cn/problems/valid-sudoku
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

 

 

class Solution {

    public boolean isValidSudoku(char[][] board) {

        // 记录某行，某位数字是否已经被摆放

        boolean[][] row = new boolean[9][9];

        // 记录某列，某位数字是否已经被摆放

        boolean[][] col = new boolean[9][9];

        // 记录某 3x3 宫格内，某位数字是否已经被摆放

        boolean[][] block = new boolean[9][9];

        for (int i = 0; i < 9; i++) {

            for (int j = 0; j < 9; j++) {

                if (board[i][j] != '.') {

                    int num = board[i][j] - '1';

                    int blockIndex = i / 3 * 3 + j / 3;

                    if (row[i][num] || col[j][num] || block[blockIndex][num]) {

                        return false;

                    } else {

                        row[i][num] = true;

                        col[j][num] = true;

                        block[blockIndex][num] = true;

                    }

                }

            }

        }

        return true;

    }

}