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.

思路：字符串每个字符的次数统计，且需根据上一个求出下一个，所以需要两个string。

time之所以最大值为3，是因为若两个不同的值组合如12--》1112，而两个相同值11--》21.

class Solution {
public:
    char Myitoa(int a)
    {
        return a+'0';
    }
    string countAndSay(int n) {
        string s="1";
        string res;
        int time=1;
        if(n==1) return s;
        while(n-1)
        {
            --n;
            res.clear();
            int len=s.size();
            for(int i=0;i<len;++i)
            {   
                if(i!=len-1&&s[i]==s[i+1]) 
                    ++time;
                else{
                    res.push_back(Myitoa(time));//time是数字,且在1-3之间
                    res.push_back(s[i]);
                    time=1;
                }
            }
            s.clear();
            s=res;
        }
        return res;
    }
};