Compilare: main.cpp: In member function 'void Dsu::undo(int)': main.cpp:28:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; upd.size() > nr; upd.pop_back()) { ~~~~~~~~~~~^~~~ main.cpp: In function 'int main()': main.cpp:74:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("colors2.in", "r", stdin); ^ main.cpp:75:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("colors2.out", "w", stdout); ^