blah.cpp

std::string reverse_domain2(const std::string& s) {
    std::string result;
    auto index = 0;

    for (const auto& c : s) {
        if (c == '.') {
            index = 0;
            result.insert(result.begin() + index, '.');
            continue;
        }

        result.insert(result.begin() + index, c);
        index++;
    }

    return result;
}

std::string reverse_domain3(std::string& copy) {
    std::reverse(copy.begin(), copy.end());
    auto start = 0;

    auto size = copy.size();

    for (auto i = 0; i <= size; i++) {
        if (copy[i] != '.' && i != size) continue;

        std::reverse(copy.begin() + start, copy.begin() + i);
        start = i + 1;
    }

    return copy;
}

std::string reverse_domain(const std::string& s) {
    std::stringstream ss(s);
    std::string segment;
    std::vector<std::string> breakList;

    while (std::getline(ss, segment, '.')) {
        breakList.push_back(segment);
    }

    std::string result;

    auto size = breakList.size();

    for (int i = size - 1; i >= 0; --i) {
        result += breakList[i];

        if (i != size - 1) {
            result += ".";
        }
    }

    return result;
}