/in/foo.cc: In function 'bool update(int)':
/in/foo.cc:24:13: error: reference to 'hash' is ambiguous
     int tmp=hash(x);
             ^~~~
/in/foo.cc:20:12: note: candidates are: int hash(int)
 inline int hash(int x) {
            ^~~~
In file included from /usr/include/c++/6/bits/basic_string.h:5643:0,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~
/in/foo.cc: In function 'int bfs(int, int)':
/in/foo.cc:66:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^