/in/foo.cc: In function 'void add(int, int, int)':
/in/foo.cc:22:5: error: reference to 'next' is ambiguous
     next[tot]=head[x];
     ^~~~
/in/foo.cc:8:5: note: candidates are: int next [6000000]
 int next[6000000];
     ^~~~
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:3:
/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:27:5: error: reference to 'next' is ambiguous
     next[tot]=head[y];
     ^~~~
/in/foo.cc:8:5: note: candidates are: int next [6000000]
 int next[6000000];
     ^~~~
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:3:
/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 'bool bfs(int, int)':
/in/foo.cc:43:33: error: reference to 'next' is ambiguous
         for(int i=head[now];i;i=next[i])
                                 ^~~~
/in/foo.cc:8:5: note: candidates are: int next [6000000]
 int next[6000000];
     ^~~~
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:3:
/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 dfs(int, int)':
/in/foo.cc:63:27: error: reference to 'next' is ambiguous
     for(int i=head[x];i;i=next[i])
                           ^~~~
/in/foo.cc:8:5: note: candidates are: int next [6000000]
 int next[6000000];
     ^~~~
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:3:
/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:130:27: error: reference to 'next' is ambiguous
     for(int i=head[S];i;i=next[i])
                           ^~~~
/in/foo.cc:8:5: note: candidates are: int next [6000000]
 int next[6000000];
     ^~~~
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:3:
/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:134:27: error: reference to 'next' is ambiguous
     for(int i=head[T];i;i=next[i])
                           ^~~~
/in/foo.cc:8:5: note: candidates are: int next [6000000]
 int next[6000000];
     ^~~~
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:3:
/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
     ^~~~