foo.cc: In function 'void dfs(int, int, int)':
foo.cc:55:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   55 |  for(int i = 0;i < bcc[s].size();i++){
      |                ~~^~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:78:10: error: too few arguments to function 'void dfs(int, int, int)'
   78 |  dfs(px,0);
      |          ^
foo.cc:42:6: note: declared here
   42 | void dfs(int s,int fa,int ans){
      |      ^~~

[Hydro](https://hydro.ac)提供评测服务