foo.cc: In function ‘int main()’:
foo.cc:25:16: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   25 |     if(fa[root]=-1)
      |        ~~~~~~~~^~~
foo.cc:28:18: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   28 |     for(int i=0;i<g[mx].size();i++)
      |                 ~^~~~~~~~~~~~~