Compilare: user.cpp: In function ‘void fft(std::vector<int>&, std::vector<int>&, std::vector<int>&)’: user.cpp:64:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while( (n >> 1) < max( a.size(), b.size() ) ) ^ user.cpp: In function ‘void solve()’: user.cpp:101:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < res.size(); i ++ ) { ^