class Solution {public:    bool isValidSudoku(vector<vector<char> > &board) {        size_t row_cnt = board.size();        size_t col_cnt = board[0].size();                vector<vector<unordered_set<char>>> subbox_rec; subbox_rec.resize(row_cnt/3);        for (int i = 0; i < row_cnt/3; i++)            subbox_rec[i].resize(col_cnt/3);        vector<unordered_set<char>> row_rec; row_rec.resize(row_cnt);        vector<unordered_set<char>> col_rec; col_rec.resize(col_cnt);        for (int j = 0; j < row_cnt; j ++)        for (int i = 0; i < col_cnt; i++)        {            char c = board[j][i];            if (c != ‘.‘)            {                //    Row                if (row_rec[j].find(c) == row_rec[j].end())                    row_rec[j].insert(c);                else return false;                //    Col                if (col_rec[i].find(c) == col_rec[i].end())                    col_rec[i].insert(c);                else return false;                //    subbox                unordered_set<char> &sb = subbox_rec[j / 3][i / 3];                if (sb.find(c) == sb.end())                    sb.insert(c);                else return false;            }        }        return true;    }};