/in/foo.cc: In function 'void spfa()':
/in/foo.cc:27:31: error: reference to 'next' is ambiguous
         for(int i=head[x];i;i=next[i])
                               ^~~~
/in/foo.cc:10:19: note: candidates are: int next [300005]
 int head[N],go[N],next[N],val[N];
                   ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/algorithm:61,
                 from /in/foo.cc:2:
/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 add(int, int, int)':
/in/foo.cc:61:5: error: reference to 'next' is ambiguous
     next[tot]=head[x];
     ^~~~
/in/foo.cc:10:19: note: candidates are: int next [300005]
 int head[N],go[N],next[N],val[N];
                   ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/algorithm:61,
                 from /in/foo.cc:2:
/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
     ^~~~