#include <iostream>
#include <iomanip>
#include <random>
#include <sstream>

std::string uuid4_generate(int len) {
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_int_distribution<> distrib(0, 15);

    std::stringstream ss;
    for (int i = 0; i < len; i++) {
        const int rand_num = distrib(gen);
        ss << std::hex << rand_num;
    }

    return ss.str();
}