foo.cc: In function 'int main()':
foo.cc:75:17: error: reference to 'end' is ambiguous
   75 |     Dfront=_max,end=id;//求出造第一条路时的树的直径——Dfront
      |                 ^~~
In file included from stdc++.h:95:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1253:5: note: candidates are: 'template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)'
 1253 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1237:5: note:                 'template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)'
 1237 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:100:5: note:                 'template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])'
  100 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:81:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(const _Container&)'
   81 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:71:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(_Container&)'
   71 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:36,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/initializer_list:101:5: note:                 'template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)'
  101 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
foo.cc:19:41: note:                 'int end'
   19 | int len,x,y,_max,id,Dfront,Dafter,start,end,fr[maxn]={},dis[maxn]={};
      |                                         ^~~
foo.cc:80:23: error: reference to 'end' is ambiguous
   80 |     dfs_for_D(start,0,end);//记录直径——Dfront上的点
      |                       ^~~
In file included from stdc++.h:95:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1253:5: note: candidates are: 'template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)'
 1253 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1237:5: note:                 'template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)'
 1237 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:100:5: note:                 'template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])'
  100 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:81:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(const _Container&)'
   81 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:71:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(_Container&)'
   71 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:36,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/initializer_list:101:5: note:                 'template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)'
  101 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
foo.cc:19:41: note:                 'int end'
   19 | int len,x,y,_max,id,Dfront,Dafter,start,end,fr[maxn]={},dis[maxn]={};
      |                                         ^~~
foo.cc:81:11: error: reference to 'end' is ambiguous
   81 |     __map[end]=1;
      |           ^~~
In file included from stdc++.h:95:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1253:5: note: candidates are: 'template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)'
 1253 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1237:5: note:                 'template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)'
 1237 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:100:5: note:                 'template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])'
  100 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:81:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(const _Container&)'
   81 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:71:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(_Container&)'
   71 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:36,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/initializer_list:101:5: note:                 'template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)'
  101 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
foo.cc:19:41: note:                 'int end'
   19 | int len,x,y,_max,id,Dfront,Dafter,start,end,fr[maxn]={},dis[maxn]={};
      |                                         ^~~
foo.cc:83:24: error: reference to 'end' is ambiguous
   83 |     for(int i=start;i!=end;i=fr[i])
      |                        ^~~
In file included from stdc++.h:95:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1253:5: note: candidates are: 'template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)'
 1253 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/valarray:1237:5: note:                 'template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)'
 1237 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:100:5: note:                 'template<class _Tp, long unsigned int _Nm> _Tp* std::end(_Tp (&)[_Nm])'
  100 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:81:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(const _Container&)'
   81 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:71:5: note:                 'template<class _Container> decltype (__cont.end()) std::end(_Container&)'
   71 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
In file included from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/range_access.h:36,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/string:54,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/istream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/sstream:38,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/complex:45,
                 from /nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/ccomplex:39,
                 from stdc++.h:54:
/nix/store/jdc41bl531bw84wi82y6gvij34q5m24a-gcc-11.3.0/include/c++/11.3.0/initializer_list:101:5: note:                 'template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)'
  101 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
foo.cc:19:41: note:                 'int end'
   19 | int len,x,y,_max,id,Dfront,Dafter,start,end,fr[maxn]={},dis[maxn]={};
      |                                         ^~~

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Found 12 testcases.
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