/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:28:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<g[pos].size();i++)
              ~^~~~~~~~~~~~~~
/in/foo.cc: In function 'bool spfa()':
/in/foo.cc:58:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<g[ q[head] ].size();i++)
               ~^~~~~~~~~~~~~~~~~~~~