Count and Say

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 111221, ...

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.

Given an integer n, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

题目的意思是按照一定的规则出现数字，以字符串的形式。规定第一个是1，接下去就是按照前一个数的读法记录，所以第二个就是1个1，记录为11，那第三个就是对11的读法就是2个1，记录为21，第四个就是对21的读法，一个2一个1，记录为1211，一次类推估计应该知道什么意思了吧。

Solution:

class Solution {
public:
    string countAndSay(int n) {
        string res = "1";  
        while(1<n--) {  
            stringstream s;  
            char last = res[0];  
            int count = 0;  
            for(int i=0;i<=res.size();i++) {  
                if(res[i] == last) {  
                    count++;  
                    continue;  
                } else {  
                    s<<count<<last;  
                    last = res[i];   
                    count = 1;  
                }  
            }  
            res = s.str();  
        }  
        return res;
    }
};