/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:10:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |         for(int i=0;i<v[n].size();i++){
      |                     ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:31:20: warning: use of an operand of type 'bool' in 'operator++' is deprecated [-Wdeprecated]
   31 |                 f[x]++;//x结点取反次数,可抵消
      |                 ~~~^