数据结构算法操作试题(C++/Python)——报数

class Solution(object):
    def countAndSay(self, n):
        """
        :type n: int
        :rtype: str
        """
        if n == 1: return "1"
        else:
            return self.retRes(self.countAndSay(n - 1))
            
    def retRes(self, str_):
        pre = res = cnt = ""
        for i in range(len(str_)):
            if pre != str_[i]:
                res = res + str(cnt) + pre
                pre = str_[i]
                cnt = 1
            else: cnt += 1
        res = res + str(cnt) + pre
        return res