小知识，大挑战！本文正在参与“程序员必备小知识”创作活动。

题目描述

请你判断一个 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。（请参考示例图）数独部分空格内已填入了数字，空白格用 '.' 表示。

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。

Untitled

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：

[["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] 是一位数字或者 '.'

题解

先对每行和每列进行统计,通过mhashSet进行是否重复的判断

再将数组拆分成3x3 的小数组,然后在小数组内进行重复的判断

char temp1 = '.';
        char temp2 = '.';
        for (int i = 0; i < 9 ; i++) {
            HashSet<Character> heng = new HashSet<>();
            HashSet<Character> zong = new HashSet<>();
            for (int j = 0; j < 9; j++) {
                temp2 = board[j][i];
                temp1 = board[i][j];
                if(temp2 !='.') {
                    // 对每列进行判断
                    if (!zong.add(board[j][i])) {
                        return false;
                    }
                }
                if (temp1 != '.') {
                    //对每行进行判断
                    if (!heng.add(board[i][j])) {
                        return false;
                    }
                }
            }
        }
        // 两个变量用于记录处于第几个单元格
        int hengCount = 0;
        // 分割成9个单元
        for (int i = 0; i < 9; i+=3) {
            // 记录列的单元数变量要放在记录横单元数循环内,否则恒循环时会溢出
            int zongCount = 0;
            for (int j = 0; j < 9; j+=3) {
                HashSet<Character> characters = new HashSet<>();
                // 对
                for (int x = 0; x < 3; x++) {
                    for (int y = 0; y < 3; y++) {
                        temp1 = board[x+hengCount][y+zongCount];
                        if(temp1 !='.') {
                            // 对每列进行判断
                            if (!characters.add(temp1) ) {
                                return false;
                            }
                        }
                    }
                }
                zongCount+=3;
            }
            hengCount+=3;
        }
        return true;

leetcode 36. 有效的数独

题目描述

题解