foo.cc: In function 'void insert(std::__cxx11::string, int, int)':
foo.cc:17:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (m<s.size()-1) insert (s, m+1, to[fa][s[m]-'a']);
       ~^~~~~~~~~~~
foo.cc:23:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (m<s.size()-1) insert(s, m+1, num);
       ~^~~~~~~~~~~
foo.cc: In function 'void dfs(int, int)':
foo.cc:43:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (m==q.size()){check();return;}
      ~^~~~~~~~~~

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