foo.cc: In function 'int main()':
foo.cc:47:17: error: reference to 'hash' is ambiguous
   47 |             a = hash(a - 1);//important
      |                 ^~~~
In file included from /usr/include/c++/9/bits/basic_string.h:6722,
                 from /usr/include/c++/9/string:55,
                 from /usr/include/c++/9/bits/locale_classes.h:40,
                 from /usr/include/c++/9/bits/ios_base.h:41,
                 from /usr/include/c++/9/ios:42,
                 from /usr/include/c++/9/ostream:38,
                 from /usr/include/c++/9/iostream:39,
                 from foo.cc:1:
/usr/include/c++/9/bits/functional_hash.h:58:12: note: candidates are: 'template<class _Tp> struct std::hash'
   58 |     struct hash;
      |            ^~~~
foo.cc:16:5: note:                 'int hash(int)'
   16 | int hash(int x)//构建哈希表
      |     ^~~~
foo.cc:48:17: error: reference to 'hash' is ambiguous
   48 |             b = hash(b);//important
      |                 ^~~~
In file included from /usr/include/c++/9/bits/basic_string.h:6722,
                 from /usr/include/c++/9/string:55,
                 from /usr/include/c++/9/bits/locale_classes.h:40,
                 from /usr/include/c++/9/bits/ios_base.h:41,
                 from /usr/include/c++/9/ios:42,
                 from /usr/include/c++/9/ostream:38,
                 from /usr/include/c++/9/iostream:39,
                 from foo.cc:1:
/usr/include/c++/9/bits/functional_hash.h:58:12: note: candidates are: 'template<class _Tp> struct std::hash'
   58 |     struct hash;
      |            ^~~~
foo.cc:16:5: note:                 'int hash(int)'
   16 | int hash(int x)//构建哈希表
      |     ^~~~

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