36. 有效的数独

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。

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 '.'

题解

java

public boolean isValidSudoku(char[][] board) {
    // 使用hash表记录出现的字符
    // key表示第n行、第n列、第n个3X3块中出现的数字
    // 0~8表示行
    // 9~17表示列
    // 18~26表示3X3块
    Map<Integer, Set<Character>> snapshot = new HashMap<>(9);
    IntStream.range(0, 27)
        .forEach(index -> snapshot.put(index, new HashSet<>(9)));

    // 遍历行列所在3X3块 移除出现的字符
    for (int i = 0; i < 9; i++) {
        for (int j = 0; j < 9; j++) {
            // 所属列
            int column = j + 9;
            // 所属第n个3X3块
            int block = (i / 3) * 3 + j / 3 + 18;
            if ('.' != board[i][j] && (
                !snapshot.get(i).add(board[i][j])
                    // 对应列存在该字符
                    || !snapshot.get(column).add(board[i][j])
                    // 对应3X3块存在该字符
                    || !snapshot.get(block).add(board[i][j]))) {
                return false;
            }
        }
    }

    return true;
}

public boolean isValidSudoku1(char[][] board) {
    // 行、列、3X3是否已经存在某个数字
    BiFunction<Integer, Integer, Boolean> isExists = (row, column) -> {
        char current = board[row][column];
        // 遍历指定行 移除出现的字符
        for (int i = 0; i < 9; i++) {
            if (column != i && board[row][i] == current) {
                return true;
            }
        }
        // 遍历指定列 移除出现字符
        for (int i = 0; i < 9; i++) {
            if (row != i && board[i][column] == current) {
                return true;
            }
        }
        // 遍历开始行列
        int startRow = row - row % 3, startColumn = column - column % 3;
        // 遍历行列所在3X3块 移除出现的字符
        for (int i = startRow; i < startRow + 3; i++) {
            for (int j = startColumn; j < startColumn + 3; j++) {
                if (i != row && j != column && board[i][j] == current) {
                    return true;
                }
            }
        }

        return false;
    };

    for (int i = 0; i < 9; i++) {
        for (int j = 0; j < 9; j++) {
            if (board[i][j] != '.' && isExists.apply(i, j)) {
                return false;
            }
        }
    }

    return true;
}

36. 有效的数独 ​

题目 ​

题解 ​

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