leetcode|中等:36. 有效的数独

1.题目

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。

1. 数字 1-9 在每一行只能出现一次。
2. 数字 1-9 在每一列只能出现一次。
3. 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 '.'

2. 题解

2.1 思路分析

思路1：题目比较简单 暴力遍历即可

2.2 代码实现

• 思路1：

class Solution {
    public boolean isValidSudoku(char[][] board) {
        // 0.计数数组
        int[] counter = new int[9];

        // 1.数字 1-9 在每一行只能出现一次。
        for (int i = 0; i < 9; i++) {
            Arrays.fill(counter,0);
            for (int j = 0; j < 9; j++) {
                if(board[i][j]!='.'){
                    int index = board[i][j]-'1';
                    counter[index]++;
                    if(counter[index]>1){
                        return false;
                    }
                }
            }
        }

        // 2.数字 1-9 在每一列只能出现一次。
        for (int i = 0; i < 9; i++) {
            Arrays.fill(counter,0);
            for (int j = 0; j < 9; j++) {
                if(board[j][i]!='.'){
                    int index = board[j][i]-'1';
                    counter[index]++;
                    if(counter[index]>1){
                        return false;
                    }
                }
            }
        }

        // 3.数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                Arrays.fill(counter,0);
                int x_offset = 3*i;
                int y_offset = 3*j;

                for (int k = 0; k < 3; k++) {
                    for (int l = 0; l < 3; l++) {
                        if(board[x_offset+k][y_offset+l]!='.'){
                            int index = board[x_offset+k][y_offset+l]-'1';
                            counter[index]++;
                            if(counter[index]>1){
                                return false;
                            }
                        }
                    }
                }
            }
        }

        return true;
    }
}

2.3 提交结果

参考资料

1. https://leetcode-cn.com/problems/valid-sudoku/