foo.cc: In function 'int dfs(int)':
foo.cc:48:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<p[x].size();i++){
              ~^~~~~~~~~~~~
foo.cc:55:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^

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