题目链接：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 ‘.’.

Note:

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

这道题的要求是检测数独是否有效，其中空位置用‘.’填充，部分填充的只检测有数字的部分。

这道题比较简单，可以使用3个数组记录每行、每列、每个九宫格出现过的数字，然后遍历数独的数组即可。遇到数字时，检测对应行、对应列以及对应九宫格是否已经出现过该数字，如果出现，返回false；否则，将对应行、对应列以及对应九宫格的该数字位置标记为1。

时间复杂度：O(n2)

空间复杂度：O(n2)

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class Solution
{
public:
    bool isValidSudoku(vector<vector<char> > &board)
    {
        int used1[9][9] = {0}, used2[9][9] = {0}, used3[9][9] = {0};
        
        for(int i = 0; i < board.size(); ++ i)
            for(int j = 0; j < board[i].size(); ++ j)
                if(board[i][j] != '.')
                {
                    int num = board[i][j] - '0' - 1, k = i / 3 * 3 + j / 3;
                    if(used1[i][num] || used2[j][num] || used3[k][num])
                        return false;
                    used1[i][num] = used2[j][num] = used3[k][num] = 1;
                }
        
        return true;
    }
};