Description

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.

Note

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

Example

Input: s = “abcdefg”, k = 2 Output: “bacdfeg”

Code

class Solution(object): def reverseStr(self, s, k): """ :type s: str :type k: int :rtype: str """ s_len = len(s) ans = "" for i in range(0, s_len, 2 * k): if i == 0: ans += s[i+k-1::-1] else: ans += s[i+k-1:i-1:-1] ans += s[i+k:i+2*k] return ans