/in/foo.cc: In function 'void spfa()':
/in/foo.cc:28:26: error: reference to 'next' is ambiguous
   for (int p=head[x];p;p=next[p])
                          ^~~~
/in/foo.cc:14:28: note: candidates are: int next [200020]
 int to[2*maxm],len[2*maxm],next[2*maxm],head[maxn],q[maxn];
                            ^~~~
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:5:
/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 addedge(int, int, int)':
/in/foo.cc:58:29: error: reference to 'next' is ambiguous
  num++;to[num]=y;len[num]=z;next[num]=head[x];head[x]=num;
                             ^~~~
/in/foo.cc:14:28: note: candidates are: int next [200020]
 int to[2*maxm],len[2*maxm],next[2*maxm],head[maxn],q[maxn];
                            ^~~~
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:5:
/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
     ^~~~