Reverse String II
Created: March 12, 2020 by [lek-tin]
Last updated: March 12, 2020
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]
Solution
class Solution:
def reverseStr(self, s: str, k: int) -> str:
start = 0
N = len(s)
s = list(s)
while start < N:
left, right = start, min(start+k-1, N-1)
start += 2*k
while left < right:
temp = s[right]
s[right] = s[left]
s[left] = temp
left += 1
right -= 1
return "".join(s)