day35

Question of the day: https://leetcode.com/problems/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 leave the rest as they are.

Example:

Input: s = "abcdefg", k = 2  
Output: "bacdfeg"  

Restrictions:

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

Ideas

1. break the sting into chunks of length 2k
2. reverse up to the first k of each chunk
3. join the chunks together and return the result

Although I logically want to break the string up into 2k chunks right away, I can just use some pointers as I move down the string so that I don't allocate too much unnecessary memory. Reversing the relevant indices and returning at the end will take O(n) runtime and O(1) space.

Code

Python

Follow-up

Try writing this in C.