[LeetCode] Count and Say

class Solution {
public:
    string countAndSay(int n) {
        string result("1");
        string pre(result);
        for(int i=1;i<n;i++){
            int len = pre.size();
            result.clear();
            for(int j=0;j<len;){
                char cur = pre[j];
                int start = j;
                j++;
                while(j<len && cur == pre[j])
                    j++;
                int end = j;
                int num = end - start;
                result += intToS(num);
                result.push_back(pre[start]);

            
            }//end for
           pre = result;
        }//end for
        return result;
    }//end func
private:
    string intToS(int n){
        ostringstream os;
        os<<n;
        string s;
        s = os.str();
        return s;
    }
};