[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 nth sequence.

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

Analysis:

class Solution {
public:
    string countAndSay(int n) {
        string str = "1";
        
        for(int i=1; i< n; i++)
        {
            string tmp;
            int count = 1;
            for(int j=1; j< =str.size(); j++)
            {
                //1. using str.size() as flag to handle remaining chars
                //2. if current value is not equal to previous one, then reset the count and save the current counting
                if (j ==str.size() || str[j] != str[j-1])
                {
                    tmp.push_back(count+'0');
                    tmp.push_back(str[j-1]);
                    count = 1;
                }
                else 
                    count++;
            }
            str = tmp;
        }
        
        return str;
    }
};