/in/foo.cc: In function 'int main()':
/in/foo.cc:20:26: error: reference to 'rank' is ambiguous
     for(int i=1;i<=n;i++)rank[a[i].p]=i;
                          ^~~~
/in/foo.cc:10:7: note: candidates are: int rank [40001]
 int n,rank[40001];//排序后每个点的位置
       ^~~~
In file included from /usr/include/c++/6/bits/move.h:57:0,
                 from /usr/include/c++/6/bits/nested_exception.h:40,
                 from /usr/include/c++/6/exception:173,
                 from /usr/include/c++/6/ios:39,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/type_traits:1482:12: note:                 template<class> struct std::rank
     struct rank
            ^~~~
/in/foo.cc:27:15: error: reference to 'rank' is ambiguous
     int ans=a[rank[1]].v;
               ^~~~
/in/foo.cc:10:7: note: candidates are: int rank [40001]
 int n,rank[40001];//排序后每个点的位置
       ^~~~
In file included from /usr/include/c++/6/bits/move.h:57:0,
                 from /usr/include/c++/6/bits/nested_exception.h:40,
                 from /usr/include/c++/6/exception:173,
                 from /usr/include/c++/6/ios:39,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/type_traits:1482:12: note:                 template<class> struct std::rank
     struct rank
            ^~~~
/in/foo.cc:30:15: error: reference to 'rank' is ambiguous
         int x=rank[i];
               ^~~~
/in/foo.cc:10:7: note: candidates are: int rank [40001]
 int n,rank[40001];//排序后每个点的位置
       ^~~~
In file included from /usr/include/c++/6/bits/move.h:57:0,
                 from /usr/include/c++/6/bits/nested_exception.h:40,
                 from /usr/include/c++/6/exception:173,
                 from /usr/include/c++/6/ios:39,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/type_traits:1482:12: note:                 template<class> struct std::rank
     struct rank
            ^~~~