LeetCode 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 = 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]
给一个字符串以及整数k，每2k个分一组，前k个倒置后k个不变。
不得不说python大法好。

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