[LC] 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]

class Solution {
    public String reverseStr(String s, int k) {
        int i = 0;
        char[] charArr = s.toCharArray();
        while (i < charArr.length) {
            int j = Math.min(i + k - 1, charArr.length - 1);
            swap(i, j, charArr);
            i += 2 * k;
        }
        return new String(charArr);
    }

    private void swap(int i, int j, char[] charArr) {
        while (i < j) {
            char temp = charArr[i];
            charArr[i] = charArr[j];
            charArr[j] = temp;
            i += 1;
            j -= 1;
        }
    }
}