38. 外观数列

链接：38. 外观数列

题解：

class Solution {
public:
    string countAndSay(int n) {
        int begin = 0;
        std::string result = "1";
        dfs(begin, n, result);
        return result;
    }
    void dfs(int begin, int n, std::string& result) {
        if (begin >= n-1) {
            return;
        }
        int i = 0;
        std::string tmp;
        // 计算下一层输入字符串
        while (i < result.size()) {
            int cnt = 0;
            char t = result[i];
            while (i < result.size()) {
                if (result[i] != t) {
                    break;
                }
                ++i;
                ++cnt;
            }
            tmp += std::to_string(cnt) + t;
        }
        result = tmp;
        dfs(begin+1, n, result);
    }
};