LeetCode: 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 n^th sequence.

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

class Solution {public:    string countAndSay(int n) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        string str = "1";        for (int i = 1; i < n; ++i)        {            string tmp;                        int count = 1;            char ch = str[0];            for (int j = 1; j < str.size(); ++j)            {                if (str[j] == ch)                    ++count;                else                {                    tmp.insert(tmp.end(), char(count+'0'));                    tmp.insert(tmp.end(), ch);                    ch = str[j];                    count = 1;                }            }            tmp.insert(tmp.end(), char(count+'0'));            tmp.insert(tmp.end(), ch);            str = tmp;        }        return str;    }};