/in/foo.cc: In function 'void addEdge(int, int, int)':
/in/foo.cc:15:5: error: reference to 'next' is ambiguous
     next[cnt]=head[u];head[u]=cnt;
     ^~~~
/in/foo.cc:8:36: note: candidates are: int next [2000020]
 int head[MAXN],e[MAXN*2],w[MAXN*2],next[MAXN*2],size[MAXN];
                                    ^~~~
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 dfs(int)':
/in/foo.cc:22:27: error: reference to 'next' is ambiguous
     for(int i=head[u];i;i=next[i])
                           ^~~~
/in/foo.cc:8:36: note: candidates are: int next [2000020]
 int head[MAXN],e[MAXN*2],w[MAXN*2],next[MAXN*2],size[MAXN];
                                    ^~~~
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
     ^~~~