541. Reverse String II

class Solution(object):    def reverseStr(self, s, k):        """        :type s: str        :type k: int        :rtype: str        """        def reverse(string):            return string[::-1]        if len(s) < k:            return s[::-1]        elif (len(s)>k) and (len(s)<2*k):            return reverse(s[:k]) + s[k:]        else:            return reverse(s[:k])+s[k:2*k]+self.reverseStr(s[2*k:],k)

• 递归的思想，分段考虑