foo.cc: In function 'void Kahn()':
foo.cc:19:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int, std::allocator<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   19 |         for(int i=0;i<edge[cur].size();i++){//vector遍历范式
      |                     ~^~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:30:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   30 |     scanf("%d%d",&n,&m);
      |     ~~~~~^~~~~~~~~~~~~~
foo.cc:34:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   34 |         scanf("%d%d",&x,&y);
      |         ~~~~~^~~~~~~~~~~~~~

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