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:

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

Code (Java):

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class Solution {     public String reverseStr(String s, int k) {         if (k <= 1) {             return s;         }           char[] charArr = s.toCharArray();         int start = 0;         int end = 0;           while (start < charArr.length) {             end = Math.min(start + k - 1, charArr.length - 1);             reverse(charArr, start, end);               start += k * 2;         }           return new String(charArr);     }       private void reverse(char[] charArr, int start, int end) {         while (start < end) {             char temp = charArr[start];             charArr[start] = charArr[end];             charArr[end] = temp;               start++;             end--;         }     } }