Compilare: user.cpp: In function ‘void df(int, int)’: user.cpp:15:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a[k].size(); ++i) ^ user.cpp:17:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < a[a[k][i].first].size(); ++j) ^ user.cpp: In function ‘int main()’: user.cpp:80:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < sol.size(); ++i) ^