541. Reverse String II

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 = 2Output: "bacdfeg

code:

class Solution(object):    def reverseStr(self, s, k):        """        :type s: str        :type k: int        :rtype: str        """        s=list(s)        for i in xrange(0,len(s),2*k):            s[i:i+k]=s[i:i+k][::-1]        return "".join(s)