Derivative

#include<iostream>
#include<map>
#include<string>
#include<sstream>
#include<regex>

std::string derivative(std::string polynomial) {
    std::regex m("[+]?([-]?[0-9]*)[\\*]?(x?)[\\^]?([0-9]*)");
    std::smatch sm;
    std::map<int, int> pow_k;

    while(regex_search(polynomial, sm, m) && polynomial.size() > 0)
    {
        int k = atoi(std::string(sm[1]).c_str());
        int pow = atoi(std::string(sm[3]).c_str());
        if (std::string(sm[2]) == "x")
        {
            if (pow == 0) pow = 1;
            if (k == 0) k = 1;
            if (std::string(sm[1]) == "-") k = -1;
        }

        pow_k[pow] += k;
        polynomial = sm.suffix();
    }

    std::ostringstream result;
    auto begin = pow_k.rbegin();
    auto end = pow_k.rend();
    auto gets = [](int pow, int k){
        std::ostringstream member;
        member << k * pow;
        if (pow > 1) member << "*x";
        if (pow > 2) member << '^' << pow-1;
        return member.str();
    };
    if (begin != end)
    {
        result << gets( begin->first, begin->second );
        ++begin;
    }
    for(; begin != end; ++begin)
    {
        if ( begin->first == 0 ) continue;
        if ( begin->second > 0 ) result << '+';
            result << gets( begin->first, begin->second );
    }
    return result.str();
}

int main()
{
#ifdef AZHUKOV
    freopen("input.txt", "r", stdin);
#endif
    std::string in;
    std::cin >> in;
    std::cout << derivative(in) << std::endl;
    return 0;
}