foo.cc:15:1: error: ISO C++ forbids declaration of 'dfs' with no type [-fpermissive]
   15 | dfs(int r,int p)
      | ^~~
foo.cc: In function 'int dfs(int, int)':
foo.cc:31:1: warning: no return statement in function returning non-void [-Wreturn-type]
   31 | }
      | ^

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