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:18:8: error: reference to 'end' is ambiguous
   else end[to[fa][s[m]-'a']]=true;
        ^~~
foo.cc:7:6: note: candidates are: bool end [100001]
 bool end[100001];
      ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95:0,
                 from foo.cc:1:
/usr/include/c++/7/valarray:1231:5: note:                 template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)
     end(const valarray<_Tp>& __va)
     ^~~
/usr/include/c++/7/valarray:1221:5: note:                 template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)
     end(valarray<_Tp>& __va)
     ^~~
In file included from /usr/include/c++/7/string:51:0,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/range_access.h:97:5: note:                 template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])
     end(_Tp (&__arr)[_Nm])
     ^~~
/usr/include/c++/7/bits/range_access.h:78:5: note:                 template<class _Container> decltype (__cont.end()) std::end(const _Container&)
     end(const _Container& __cont) -> decltype(__cont.end())
     ^~~
/usr/include/c++/7/bits/range_access.h:68:5: note:                 template<class _Container> decltype (__cont.end()) std::end(_Container&)
     end(_Container& __cont) -> decltype(__cont.end())
     ^~~
In file included from /usr/include/c++/7/bits/range_access.h:36:0,
                 from /usr/include/c++/7/string:51,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/initializer_list:99:5: note:                 template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)
     end(initializer_list<_Tp> __ils) noexcept
     ^~~
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:24:8: error: reference to 'end' is ambiguous
   else end[num]=true;
        ^~~
foo.cc:7:6: note: candidates are: bool end [100001]
 bool end[100001];
      ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95:0,
                 from foo.cc:1:
/usr/include/c++/7/valarray:1231:5: note:                 template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)
     end(const valarray<_Tp>& __va)
     ^~~
/usr/include/c++/7/valarray:1221:5: note:                 template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)
     end(valarray<_Tp>& __va)
     ^~~
In file included from /usr/include/c++/7/string:51:0,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/range_access.h:97:5: note:                 template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])
     end(_Tp (&__arr)[_Nm])
     ^~~
/usr/include/c++/7/bits/range_access.h:78:5: note:                 template<class _Container> decltype (__cont.end()) std::end(const _Container&)
     end(const _Container& __cont) -> decltype(__cont.end())
     ^~~
/usr/include/c++/7/bits/range_access.h:68:5: note:                 template<class _Container> decltype (__cont.end()) std::end(_Container&)
     end(_Container& __cont) -> decltype(__cont.end())
     ^~~
In file included from /usr/include/c++/7/bits/range_access.h:36:0,
                 from /usr/include/c++/7/string:51,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/initializer_list:99:5: note:                 template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)
     end(initializer_list<_Tp> __ils) noexcept
     ^~~
foo.cc: In function 'int query(int)':
foo.cc:37:7: error: reference to 'end' is ambiguous
   if (end[step]) return 0;
       ^~~
foo.cc:7:6: note: candidates are: bool end [100001]
 bool end[100001];
      ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95:0,
                 from foo.cc:1:
/usr/include/c++/7/valarray:1231:5: note:                 template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)
     end(const valarray<_Tp>& __va)
     ^~~
/usr/include/c++/7/valarray:1221:5: note:                 template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)
     end(valarray<_Tp>& __va)
     ^~~
In file included from /usr/include/c++/7/string:51:0,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/range_access.h:97:5: note:                 template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])
     end(_Tp (&__arr)[_Nm])
     ^~~
/usr/include/c++/7/bits/range_access.h:78:5: note:                 template<class _Container> decltype (__cont.end()) std::end(const _Container&)
     end(const _Container& __cont) -> decltype(__cont.end())
     ^~~
/usr/include/c++/7/bits/range_access.h:68:5: note:                 template<class _Container> decltype (__cont.end()) std::end(_Container&)
     end(_Container& __cont) -> decltype(__cont.end())
     ^~~
In file included from /usr/include/c++/7/bits/range_access.h:36:0,
                 from /usr/include/c++/7/string:51,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/initializer_list:99:5: note:                 template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)
     end(initializer_list<_Tp> __ils) noexcept
     ^~~
foo.cc: In function 'void dfs(int, int)':
foo.cc:43:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (m==s.size()){check();return;}
      ~^~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。