foo.cpp: In function 'void insert(int, int)':
foo.cpp:12:13: error: reference to 'next' is ambiguous
  v[++ne]=bb;next[ne]=head[aa];head[aa]=ne;
             ^
foo.cpp:7:13: note: candidates are: int next [2000]
 int head[N],next[2000],v[N],fa[N],sum[N],a[N][N],tot[N];
             ^
In file included from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/bits/stl_algobase.h:66:0,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/bits/char_traits.h:39,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/ios:40,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/ostream:38,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/iostream:39,
                 from foo.cpp:1:
C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/bits/stl_iterator_base_funcs.h:184:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^
foo.cpp: In function 'void dfs(int)':
foo.cpp:27:24: error: reference to 'next' is ambiguous
  for(int i=head[k];i;i=next[i])if(vis[v[i]]!=cnt)
                        ^
foo.cpp:7:13: note: candidates are: int next [2000]
 int head[N],next[2000],v[N],fa[N],sum[N],a[N][N],tot[N];
             ^
In file included from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/bits/stl_algobase.h:66:0,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/bits/char_traits.h:39,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/ios:40,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/ostream:38,
                 from C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/iostream:39,
                 from foo.cpp:1:
C:/TDM-GCC-32/lib/gcc/mingw32/4.9.2/include/c++/bits/stl_iterator_base_funcs.h:184:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^