[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 = 2Output: "bacdfeg"

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

class Solution {public:    string reverseStr(string s, int k) {        for (int i = 0; i < s.size(); ) {            int j = min(i + k - 1, (int)s.size() - 1);            for (int ii = i, jj = j; ii < jj; ii++, jj--)                swap(s[ii], s[jj]);            i += 2 * k;        }        return s;    }};