原题

判断一个 9x9 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。

上图是一个部分填充的有效的数独。

数独部分空格内已填入了数字，空白格用 '.' 表示。

示例1：

输入：
[
["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1：

输入：
[
["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。

说明:

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。
给定数独序列只包含数字 1-9 和字符 '.' 。
给定数独永远是 9x9 形式的。

解法

思想

行、列、宫分别分配一个哈希集记录出现的数字。

代码

class Solution {
    char[][] globalBoard;
    //行:0-8,列:9-17,宫:18-26
    Set<Character>[] sets = new Set[27];
    public boolean isValidSudoku(char[][] board) {
        for(int i = 0;i<27;i++){
            sets[i] = new HashSet<>();
        }
        globalBoard = board;
        for(int x = 0 ; x < 9 ; x ++){
            for(int y = 0;y<9;y++){
                if(isValidSingle(x,y)==false) return false;
            }
        }
        return true;
    }
    public boolean isValidSingle(int x,int y){
        if(globalBoard[x][y]=='.') return true;
        if(sets[x].contains(globalBoard[x][y])) return false;
        sets[x].add(globalBoard[x][y]);
        if(sets[9+y].contains(globalBoard[x][y])) return false;
        sets[9+y].add(globalBoard[x][y]);
        if(sets[18+y/3*3+x/3].contains(globalBoard[x][y])) return false;
        sets[18+y/3*3+x/3].add(globalBoard[x][y]);
        return true;
    }
}

原创文章，作者：彭晨涛，如若转载，请注明出处：https://www.codetool.top/article/leetcode36-%e6%9c%89%e6%95%88%e7%9a%84%e6%95%b0%e7%8b%ac/

leetcode36-有效的数独

原题

解法

思想

代码

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