[LeetCode]--36. Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character ‘.’.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

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public class _36ValidSudoku {

    public boolean isValidSudoku(char[][] board) {
        boolean[] visited = new boolean[9];

        // row
        for (int i = 0; i < 9; i++) {
            Arrays.fill(visited, false);
            for (int j = 0; j < 9; j++) {
                if (!process(visited, board[i][j]))
                    return false;
            }
        }

        // col
        for (int i = 0; i < 9; i++) {
            Arrays.fill(visited, false);
            for (int j = 0; j < 9; j++) {
                if (!process(visited, board[j][i]))
                    return false;
            }
        }

        // sub matrix
        for (int i = 0; i < 9; i += 3) {
            for (int j = 0; j < 9; j += 3) {
                Arrays.fill(visited, false);
                for (int k = 0; k < 9; k++) {
                    if (!process(visited, board[i + k / 3][j + k % 3]))
                        return false;
                }
            }
        }
        return true;

    }

    private boolean process(boolean[] visited, char digit) {
        if (digit == '.') {
            return true;
        }

        int num = digit - '0';
        if (num < 1 || num > 9 || visited[num - 1]) {
            return false;
        }

        visited[num - 1] = true;
        return true;
    }
}

访问小范围的九宫格就有点麻烦。board[i + k / 3][j + k % 3]，用这个表示就很好。