/in/foo.cc: In function 'int main()':
/in/foo.cc:26:5: error: reference to 'hash' is ambiguous
  if(hash(0,(a.size()-1)/2)==hash(a.size(),(a.size()-1)/2)){
     ^~~~
/in/foo.cc:9:5: note: candidates are: int hash(int, int)
 int hash(int begin,int last){
     ^~~~
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:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~
/in/foo.cc:26:29: error: reference to 'hash' is ambiguous
  if(hash(0,(a.size()-1)/2)==hash(a.size(),(a.size()-1)/2)){
                             ^~~~
/in/foo.cc:9:5: note: candidates are: int hash(int, int)
 int hash(int begin,int last){
     ^~~~
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:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~