Leetcode #541 Reverse String II

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