Compilare: user.cpp: In function ‘void solve()’: user.cpp:58:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<a.size(); ++i) ~^~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:84:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("magnet.in", "r", stdin); ^ user.cpp:85:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("magnet.out", "w", stdout); ^