/in/foo.cc: In function 'int dfs(int)':
/in/foo.cc:25:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < infect[k].size(); i++) { 
                  ~~^~~~~~~~~~~~~~~~~~
/in/foo.cc:27:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < infect[k].size(); j++) {   
                   ~~^~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:47:7: warning: variable 'exist' set but not used [-Wunused-but-set-variable]
  bool exist[301] = { 0 };
       ^~~~~