/in/foo.cc: In function 'void toposort()':
/in/foo.cc:92:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i = 0; i < out[u].size(); i ++) {
                        ~~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:141:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(int k = 0; k < out[u].size(); k ++) {
                            ~~^~~~~~~~~~~~~~~