std::vector<int> permutation_positions(const std::string& s1, const std::string& s2) {
    if(s1.length() < s2.length())
        return {};

    std::map<char, int64_t> letters{};
    for(auto letter: s2) { ++letters[letter]; }
    for(size_t index = 0; index < s2.length(); ++index) {
        --letters[s1[index]];
    }

    std::vector<int> results{};
    for(size_t index = 0; index < (s1.length() - s2.length()); ++index) {
        std::cout << letters << std::endl;
        if(std::all_of(letters.begin(), letters.end(), [](const auto& pair) { return pair.second == 0; })) {
            results.push_back(index);
        }

        --letters[s1[index + s2.length()]];
        ++letters[s1[index]];
    }
    if(std::all_of(letters.begin(), letters.end(), [](const auto& pair) { return pair.second == 0; })) {
        results.push_back(s1.length() - s2.length());
    }

    return results;
}