/in/foo.cc: In function 'void MakeMinLen(int*)':
/in/foo.cc:48:9: error: reference to 'next' is ambiguous
    then=next[then];
         ^~~~
/in/foo.cc:13:20: note: candidates are: int next [500050]
 int point[N],to[M],next[M],val[M];
                    ^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/7/algorithm:61,
                 from /in/foo.cc:3:
/usr/include/c++/7/bits/stl_iterator_base_funcs.h:208:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~
/in/foo.cc: In function 'void InitGraph()':
/in/foo.cc:61:3: error: reference to 'next' is ambiguous
   next[i]=point[xu[i].v];
   ^~~~
/in/foo.cc:13:20: note: candidates are: int next [500050]
 int point[N],to[M],next[M],val[M];
                    ^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/7/algorithm:61,
                 from /in/foo.cc:3:
/usr/include/c++/7/bits/stl_iterator_base_funcs.h:208:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~
/in/foo.cc:70:3: error: reference to 'next' is ambiguous
   next[i]=point[xu[i].u];
   ^~~~
/in/foo.cc:13:20: note: candidates are: int next [500050]
 int point[N],to[M],next[M],val[M];
                    ^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/7/algorithm:61,
                 from /in/foo.cc:3:
/usr/include/c++/7/bits/stl_iterator_base_funcs.h:208:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~