class Solution {

 public:

     bool isValidSudoku(vector<vector<char> > &board) {

         // Note: The Solution object is instantiated only once.

         vector<vector<bool>> rows(, vector<bool>(,false));

         vector<vector<bool>> cols(, vector<bool>(,false));

         vector<vector<bool>> blocks(, vector<bool>(,false));

         for(int i = ; i < ; i++)

             for(int j = ; j < ; j++)

             {

                 if(board[i][j] == '.')continue;

                 int num = board[i][j] - '';

                 if(rows[i][num] || cols[j][num] || blocks[i - i% + j/][num])

                     return false;

                 rows[i][num] = cols[j][num] = blocks[i - i% + j/][num] = true;

             }

         return true;

     }

 };

 class Solution {

 public:

    string unguarded_convert(const string &say)

 {

     stringstream ss;

     int count = ;

     char last = say[];

     for (size_t i = ; i <= say.size(); ++i)

     {

         if (say[i] == last)

         {

             ++count;

         }

         else

         {

             ss << count << last;

             count = ;

             last = say[i];

         }

     }

     return ss.str();

 }

 string countAndSay(int n)

 {

     if (n <= ) return string();

     string say = "";

     for (int i = ; i < n; ++i)

     {

         say = unguarded_convert(say);

     }

     return say;

 }

 };