std::vector<int> SlowSolution(const int& number_of_lists, const int& lists_length, const VectorData& data) {
    std::vector<int> result;
    result.reserve(number_of_lists * lists_length);

    for (const auto& list: data) {
        for (const auto& element: list)
            result.push_back(element);
    }

    std::sort(result.begin(), result.end());

    return result;
}

void StressTests() {
    int number_of_iterations = 100;
    for (int it = 0; it < number_of_iterations; ++it) {
        int number_of_lists = rand() % 100 + 1;
        int list_size = rand() % 1000 + 1;
        std::vector<std::vector<int>> data(number_of_lists);

        for (size_t index = 0; index < number_of_lists; ++index) {
            std::vector<int> result;
            result.reserve(list_size);

            for (int index = 0; index < list_size; ++index) {
                result.push_back(rand() % 1000);
            }

            std::sort(result.begin(), result.end());

            data[index] = result;
        }

        std::vector<int> okResult = SlowSolution(number_of_lists, list_size, data);
        std::vector<int> myResult = SolutionWithHeap(number_of_lists, list_size, data);

        if (okResult != myResult) {
            std::cout << "number_of_lists = " << number_of_lists << ", list_size = " << list_size << "\nOk result: ";
            for (const auto &element: okResult) {
                std::cout << element << " ";
            }
            std::cout << "\nMy result: ";
            for (const auto &element: myResult) {
                std::cout << element << " ";
            }
            std::cout << "\n";
        }
    }
}