/in/foo.cc: In function 'void ljb(int, int, int)':
/in/foo.cc:20:1: error: reference to 'next' is ambiguous
 next[size]=first[A];
 ^~~~
/in/foo.cc:14:25: note: candidates are: long long int next [600001]
 long long first[100001],next[600001],v[600001],w[600001],s[100001],t[100001];
                         ^~~~
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: In function 'int main()':
/in/foo.cc:29:17: warning: format '%d' expects argument of type 'int*', but argument 2 has type 'long long int*' [-Wformat=]
 scanf("%d",&E[i]);
                 ^
/in/foo.cc:63:3: error: reference to 'next' is ambiguous
 u=next[u];
   ^~~~
/in/foo.cc:14:25: note: candidates are: long long int next [600001]
 long long first[100001],next[600001],v[600001],w[600001],s[100001],t[100001];
                         ^~~~
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
     ^~~~