[LintCode] Count and Say 计数和读法

class Solution {
public:
    /**
     * @param n the nth
     * @return the nth sequence
     */
    string countAndSay(int n) {
        if (n < 1) return "";
        string res = "1";
        while (--n) {
            res.push_back('#');
            string t = "";
            int cnt = 1;
            for (int i = 1; i < res.size(); ++i) {
                if (res[i] == res[i - 1]) ++cnt;
                else {
                    t += to_string(cnt) + res[i - 1];
                    cnt = 1;
                }
            }
            res = t;
        }
        return res;
    }
};