1 class Solution {
 2 public:
 3     bool isValidSudoku(vector<vector<char> > &board) {
 4         // Note: The Solution object is instantiated only once.
 5         vector<vector<bool>> rows(9, vector<bool>(9,false));
 6         vector<vector<bool>> cols(9, vector<bool>(9,false));
 7         vector<vector<bool>> blocks(9, vector<bool>(9,false));
 8
 9         for(int i = 0; i < 9; i++)
10             for(int j = 0; j < 9; j++)
11             {
12                 if(board[i][j] == '.')continue;
13                 int num = board[i][j] - '1';
14                 if(rows[i][num] || cols[j][num] || blocks[i - i%3 + j/3][num])
15                     return false;
16                 rows[i][num] = cols[j][num] = blocks[i - i%3 + j/3][num] = true;
17             }
18         return true;
19     }
20 };

 1 class Solution {
 2 public:
 3    string unguarded_convert(const string &say)
 4 {
 5     stringstream ss;
 6     int count = 0;
 7     char last = say[0];
 8
 9     for (size_t i = 0; i <= say.size(); ++i)
10     {
11         if (say[i] == last)
12         {
13             ++count;
14         }
15         else
16         {
17             ss << count << last;
18             count = 1;
19             last = say[i];
20         }
21     }
22
23     return ss.str();
24 }
25
26 string countAndSay(int n)
27 {
28     if (n <= 0) return string();
29
30     string say = "1";
31
32     for (int i = 1; i < n; ++i)
33     {
34         say = unguarded_convert(say);
35     }
36
37     return say;
38 }
39 };