foo.cc: In function 'void spfa(int)':
foo.cc:18:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<v[x].size();i++){
               ~^~~~~~~~~~~~
foo.cc: In function 'double dfs(int, int)':
foo.cc:35:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<v[c].size();i++)
              ~^~~~~~~~~~~~
foo.cc:39:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<v[x].size();i++)
              ~^~~~~~~~~~~~

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