力扣541. 反转字符串 II

原题

 1 class Solution:
 2     def reverseStr(self, s: str, k: int) -> str:
 3         begin,lens,ans = 0,len(s),''
 4         while begin < lens:
 5             mid = begin + k
 6             if mid >= lens:
 7                 ans += s[begin:][::-1]
 8             else:
 9                 ans += s[begin:mid][::-1]+s[mid:mid+k]
10             begin += 2 * k
11         return ans