foo.cc: In function 'void dfs2(int, int)':
foo.cc:31:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   31 |         for (int i=0;i<d[x].size();++i)
      |                      ~^~~~~~~~~~~~

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