View Compilation Error

0_0_16953986_1843.cpp: In function 'int main()':
0_0_16953986_1843.cpp:67:32: error: reference to 'hash' is ambiguous
    root[i] = insert(root[i-1], hash(a[i]));
                                ^
0_0_16953986_1843.cpp:14:5: note: candidates are: int hash(int)
 int hash(int x) {
     ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/basic_string.h:3068:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/string:52,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/random:40,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_algo.h:66,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/algorithm:62,
                 from 0_0_16953986_1843.cpp:4:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^