View Compilation Error

0_0_25940862_29235.cpp: In function 'void go2(int, int)':
0_0_25940862_29235.cpp:228:17: error: reference to 'rank' is ambiguous
         int ans=rank(root[x],a[y+1]-1);
                 ^
0_0_25940862_29235.cpp:155:9: note: candidates are: int treap::rank(treap::node*, int)
     int rank(node *x,int val)
         ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/move.h:57:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_pair.h:59,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_algobase.h:64,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/char_traits.h:39,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ios:40,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ostream:38,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/iostream:39,
                 from 0_0_25940862_29235.cpp:3:
GCC4.9.2/x86_64-w64-mingw32/include/c++/type_traits:1340:12: note:                 template<class> struct std::rank
     struct rank
            ^