foo.cc: In function ‘int main()’:
foo.cc:14:9: error: ‘nodes’ was not declared in this scope
   14 |         nodes[y]=nodes[x]=1;
      |         ^~~~~
foo.cc:35:18: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   35 |     for(int i=0;i<g[mx].size();++i)
      |                 ~^~~~~~~~~~~~~