Leetcode23: 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.

class Solution {
public:
    string countSay(string &str)
    {
        str.append("0");
        stringstream ss;
        int count = 0;
        char temp = str[0];
        for(int i = 0; i < str.size(); i++)
        {
            if(str[i] == temp)
                count++;
            else
            {
                ss << count << temp;
                count = 1;
                temp = str[i];
            }
        }
        return ss.str();
    }
    string countAndSay(int n) {
        string str = "1";
        for(int i = 1; i < n; i++)
        {
            str = countSay(str);
        }
        return str;
    }
};

之所以末尾追加一个0，是为了防止当前字符串的末尾是连续的n个相同的数，导致判断到末尾时依旧执行count++但是不写入stream流里。