Compilare: user.cpp: In function ‘std::string solve()’: user.cpp:20:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (st.size() < M) { ^ user.cpp:24:72: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (st.size() && note[i] > st.back() && N - i - 1 >= M - st.size()) { ^