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:

1. The string consists of lower English letters only.
2. Length of the given string and k will in the range [1, 10000]

class Solution(object):
    def reverseStr(self, s, k):
        """
        :type s: str
        :type k: int
        :rtype: str
        """
        n=len(s)
        i=0
        ans=''
        while i<n:
            if i+k-1>=n:
                ans+=(s[i:])[::-1]
                break
            elif i+2*k-1>=n:
                ans+=(s[i:i+k])[::-1]+s[i+k:]
                break
            else:
                ans+=(s[i:i+k])[::-1]+s[i+k:i+2*k]
                i=i+2*k
        return ans