Question：

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.

2读1，3读2，n读n-1，根据上面的规则。

Algorithm：

迭代

Accepted Code：

class Solution {
public:
    string work(string s)
    {
        int k=0;
        string t;
        while(k<s.size())
        {
            int tmp=s[k];
            int count=0;
            while(s[k]==tmp)
            {
                k++;
                count++;
            }
            t.push_back(count+'0');
            t.push_back(tmp);
        }
        return t;
    }
    string countAndSay(int n) {
        if(n==1)return "1";
        string tmp="1";
        while(--n)
        {
            tmp=work(tmp);    //迭代
        }
        return tmp;
    }
};