/in/foo.cc: In function 'int main()':
/in/foo.cc:46:13: error: reference to 'next' is ambiguous
             next[head[a[i]]]=i;
             ^~~~
/in/foo.cc:10:30: note: candidates are: int next [1000010]
 int a[maxn+10],head[maxx+10],next[maxx+10],ans[maxm+10];
                              ^~~~
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:1:
/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:61:17: error: reference to 'next' is ambiguous
             add(next[now++],1);
                 ^~~~
/in/foo.cc:10:30: note: candidates are: int next [1000010]
 int a[maxn+10],head[maxx+10],next[maxx+10],ans[maxm+10];
                              ^~~~
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:1:
/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
     ^~~~