/in/foo.cc: In function 'int main()':
/in/foo.cc:76:3: error: reference to 'next' is ambiguous
   next[pre[x]]=i;
   ^~~~
/in/foo.cc:36:10: note: candidates are: int next [500005]
 int a[N],next[N],pre[N],tree[N<<2],ans[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:88:8: error: reference to 'next' is ambiguous
     if(next[j]) add(1,1,n,next[j]);
        ^~~~
/in/foo.cc:36:10: note: candidates are: int next [500005]
 int a[N],next[N],pre[N],tree[N<<2],ans[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:88:27: error: reference to 'next' is ambiguous
     if(next[j]) add(1,1,n,next[j]);
                           ^~~~
/in/foo.cc:36:10: note: candidates are: int next [500005]
 int a[N],next[N],pre[N],tree[N<<2],ans[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
     ^~~~