foo.cpp: In function 'int dfs(int, Int64)':
foo.cpp:19:22: error: reference to 'hash' is ambiguous
  Hash::iterator it = hash.find(id);
                      ^
foo.cpp:14:6: note: candidates are: Hash hash
 Hash hash;
      ^
In file included from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.h:3033:0,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\string:52,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\random:41,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:65,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\algorithm:62,
                 from foo.cpp:1:
c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^
foo.cpp:20:12: error: reference to 'hash' is ambiguous
  if (it != hash.end()) return it->second;
            ^
foo.cpp:14:6: note: candidates are: Hash hash
 Hash hash;
      ^
In file included from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.h:3033:0,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\string:52,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\random:41,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:65,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\algorithm:62,
                 from foo.cpp:1:
c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^
foo.cpp:29:9: error: reference to 'hash' is ambiguous
  return hash[id] = now;
         ^
foo.cpp:14:6: note: candidates are: Hash hash
 Hash hash;
      ^
In file included from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.h:3033:0,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\string:52,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\random:41,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:65,
                 from c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\algorithm:62,
                 from foo.cpp:1:
c:\tdm-gcc-32\lib\gcc\mingw32\4.8.1\include\c++\bits\functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^
foo.cpp:30:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^