Compilare: user.cpp: In function ‘std::__cxx11::string solve(const string&)’: user.cpp:28:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ user.cpp:33:60: warning: ‘ch’ may be used uninitialized in this function [-Wmaybe-uninitialized] if(nrmax == 1 && fmax > (n - 1 - i) / 2) ret += char('a' + ch), --fr[ch]; ~~~~^~~~