Compilare: user.cpp: In function ‘int main()’: user.cpp:38:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 0; i <= U.size()-1; ++i ) ^ user.cpp:58:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int j = 0; j < Sol[i].size(); ++j ) ^ user.cpp:70:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 0; i < Sol2.size(); ++i ) ^