Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.
Example:
Input: s = "abcdefg", k = 2
Output: "bacdfeg"
Restrictions: 
 The string consists of lower English letters only.
 Length of the given string and k will in the range [1, 10000]
class Solution:
     def reverseStr(self, s, k):
         """
         :type s: str
         :type k: int
         :rtype: str
         """
         list_s = list(s)
         n = len(list_s)
         for i in range(0,n,2*k):
             if n-i>=k:
                 list_s[i:i+k] = reversed(list_s[i:i+k])
             elif n-i<k:
                 list_s[i:] = reversed(list_s[i:])
                 
         return ''.join(list_s)
class Solution:
     def reverseStr(self, s, k):
         """
         :type s: str
         :type k: int
         :rtype: str
         """
         list_s = list(s)
         n = len(list_s)
         for i in range(0,n,2*k):
             if n-i>=k:
                 list_s[i:i+k] = reversed(list_s[i:i+k])
             elif n-i<k:
                 list_s[i:] = reversed(list_s[i:])
                 
         return ''.join(list_s)