/in/foo.cc: In function 'void add(int, int, int)':
/in/foo.cc:32:5: error: reference to 'next' is ambiguous
     next[n]=head[x]; head[x]=n;
     ^~~~
/in/foo.cc:22:19: note: candidates are: int next [200220]
 int head[maxn<<2],next[maxn<<2];
                   ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 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 SPFA()':
/in/foo.cc:44:35: error: reference to 'next' is ambiguous
         for(int e=head[u];e!=-1;e=next[e])
                                   ^~~~
/in/foo.cc:22:19: note: candidates are: int next [200220]
 int head[maxn<<2],next[maxn<<2];
                   ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 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 'int main()':
/in/foo.cc:62:9: error: reference to 'next' is ambiguous
  memset(next,-1,sizeof(next));
         ^~~~
/in/foo.cc:22:19: note: candidates are: int next [200220]
 int head[maxn<<2],next[maxn<<2];
                   ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 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:62:24: error: reference to 'next' is ambiguous
  memset(next,-1,sizeof(next));
                        ^~~~
/in/foo.cc:22:19: note: candidates are: int next [200220]
 int head[maxn<<2],next[maxn<<2];
                   ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 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
     ^~~~