/in/foo.cc: In function 'int main()':
/in/foo.cc:48:4: error: reference to 'next' is ambiguous
    next[head[a[i]]]=i;
    ^~~~
/in/foo.cc:5:53: note: candidates are: int next [1111111]
 int m,ans[222222],n,s[50001],a[50001],head[1111111],next[1111111];
                                                     ^~~~
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:66:8: error: reference to 'next' is ambiguous
    add(next[now],1);
        ^~~~
/in/foo.cc:5:53: note: candidates are: int next [1111111]
 int m,ans[222222],n,s[50001],a[50001],head[1111111],next[1111111];
                                                     ^~~~
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
     ^~~~