541-反转字符串-ii

std::string reverseStr(std::string s, int k) {
    const int n = s.size();

    for (int i = 0; i < n; i += 2 * k) {
        int left  = i;
        int right = std::min(i + k - 1, n - 1);

        while (left < right) {
            std::swap(s[left], s[right]);
            ++left;
            --right;
        }
    }

    return s;
}