View Compilation Error

0_0_18131798_13371.cpp: In function 'void dfs()':
0_0_18131798_13371.cpp:288:14: error: reference to 'hash' is ambiguous
     string h=hash();
              ^
0_0_18131798_13371.cpp:8:8: note: candidates are: std::string hash()
 string hash()
        ^
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 0_0_18131798_13371.cpp:3:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^