Valid Sudoku

Determine whether a Sudoku is valid.

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

 Notice

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

Example

The following partially filed sudoku is valid.

分析：

class Solution {
    public boolean isValidSudoku(char[][] board) {
        Set<String> seen = new HashSet<>();
        for (int i = 0; i < 9; ++i) {
            for (int j = 0; j < 9; ++j) {
                char number = board[i][j];
                if (number != '.')
                    if (!seen.add(number + " in row " + i)
                            || !seen.add(number + " in column " + j)
                            || !seen.add(number + " in block " + i / 3 + "-" + j / 3))
                        return false;
            }
        }
        return true;
    }
}