foo.cc: In function 'int dfs(int)':
foo.cc:26:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   26 |  for (int i = 0; i < infect[k].size(); i++) {
      |                  ~~^~~~~~~~~~~~~~~~~~
foo.cc:28:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 |   for (int j = 0; j < infect[k].size(); j++) {
      |                   ~~^~~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:48:7: warning: variable 'exist' set but not used [-Wunused-but-set-variable]
   48 |  bool exist[301] = { 0 };
      |       ^~~~~
foo.cc:47:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   47 |  scanf("%d%d", &n, &p);
      |  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:52:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   52 |   scanf("%d%d", &f, &c);
      |   ~~~~~^~~~~~~~~~~~~~~~

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