LeetCode36-有效的数独

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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：

http://blog-image-creasylai.oss-cn-shenzhen.aliyuncs.com/blog.images/img/2021/1124/article1/01.png

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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：

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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 '.'

解答

看题目可知，有效的数独是指每行/每列/每个3*3的方格，均无重复元素出现。所以，答题也按这个思路去做即可

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class Solution {
    public boolean isValidSudoku(char[][] board) {
        Map<Character, Boolean>[][] maps = new HashMap[3][3];
        for (int i = 0; i < board.length; i++) {
            Map<Character, Boolean> rowMap = new HashMap<>();
            Map<Character, Boolean> columnMap = new HashMap<>();
            for (int j = 0; j < board[i].length; j++) {
                //检测行
                if(board[i][j] != '.'){
                    Boolean exists = rowMap.put(board[i][j], true);
                    if(null != exists) return false;
                }
                //检测列
                if(board[j][i] != '.'){
                    Boolean exists = columnMap.put(board[j][i], true);
                    if(null != exists) return false;
                }
                //检测矩阵
                if(board[i][j] != '.'){
                    if( null == maps[i/3][j/3] ){
                        maps[i/3][j/3] = new HashMap<>();
                    }
                    Boolean exists = maps[i/3][j/3].put(board[i][j], true);
                    if(null != exists) return false;
                }
            }
            rowMap.clear();
            columnMap.clear();
        }
        return true;
    }
}

题目转载自：https://leetcode-cn.com/problems/valid-sudoku

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