/in/foo.cc: In function 'void add(int, int, int)':
/in/foo.cc:14:9: error: reference to 'next' is ambiguous
  tot++; next[tot]=head[x]; len[tot]=z; v[tot]=y; head[x]=tot;
         ^~~~
/in/foo.cc:10:31: note: candidates are: int next [201]
 int n,m,dis[N],head[N],val[N],next[N],len[N],v[N];
                               ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:4:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:205:5: 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 dfs(int, int)':
/in/foo.cc:19:27: error: reference to 'next' is ambiguous
  for (int i=head[x]; i; i=next[i])
                           ^~~~
/in/foo.cc:10:31: note: candidates are: int next [201]
 int n,m,dis[N],head[N],val[N],next[N],len[N],v[N];
                               ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:4:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:205:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~