Language: C++

#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <unordered_map>

static std::unordered_map<std::pair<long long, long long>, long long> gcd_map;

long long gcd(long long n1, long long n2)
{
    if (n1 < n2) std::swap(n1, n2);
    if (gcd_map.find(std::make_pair(n1, n2)) != std::end(gcd_map)) {
        return gcd_map[std::make_pair(n1, n2)];
    }

    long long b = n1;
    long long s = n2;

    long long m;
    do {
        m = b % s;
        b = s;
        s = m;
    } while(m != 0);

    gcd_map[std::make_pair(n1, n2)] = b;

    return b;
}

int main()
{
    int N;
    std::cin >> N;

    std::vector<long long> A(N);
    for (int i = 0; i < N; i++) {
        std::cin >> A[i];
    }

    long long max_g = 0;
    for (int i = N-1; i >= 0; i--) {
        long long g = (i == 0) ? A[1] : A[0];
        for (int j = 0; j < N; j++) {
            if (j == i) continue;
            g = gcd(g, A[j]);
        }
        max_g = std::max(max_g, g);
    }

    std::cout << max_g << std::endl;

    return 0;
}

Compiler output:
a.cc:7:71: error: use of deleted function 'std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::unordered_map() [with _Key = std::pair<long long int, long long int>; _Tp = long long int; _Hash = std::hash<std::pair<long long int, long long int> >; _Pred = std::equal_to<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<const std::pair<long long int, long long int>, long long int> >]'
    7 | static std::unordered_map<std::pair<long long, long long>, long long> gcd_map;
      |                                                                       ^~~~~~~
In file included from /usr/include/c++/14/unordered_map:41,
                 from a.cc:5:
/usr/include/c++/14/bits/unordered_map.h:148:7: note: 'std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::unordered_map() [with _Key = std::pair<long long int, long long int>; _Tp = long long int; _Hash = std::hash<std::pair<long long int, long long int> >; _Pred = std::equal_to<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<const std::pair<long long int, long long int>, long long int> >]' is implicitly deleted because the default definition would be ill-formed:
  148 |       unordered_map() = default;
      |       ^~~~~~~~~~~~~
/usr/include/c++/14/bits/unordered_map.h:148:7: error: use of deleted function 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_Hashtable() [with _Key = std::pair<long long int, long long int>; _Value = std::pair<const std::pair<long long int, long long int>, long long int>; _Alloc = std::allocator<std::pair<const std::pair<long long int, long long int>, long long int> >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long long int, long long int> >; _Hash = std::hash<std::pair<long long int, long long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>]'
In file included from /usr/include/c++/14/bits/unordered_map.h:33:
/usr/include/c++/14/bits/hashtable.h:539:7: note: 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_Hashtable() [with _Key = std::pair<long long int, long long int>; _Value = std::pair<const std::pair<long long int, long long int>, long long int>; _Alloc = std::allocator<std::pair<const std::pair<long long int, long long int>, long long int> >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long long int, long long int> >; _Hash = std::hash<std::pair<long long int, long long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>]' is implicitly deleted because the default definition would be ill-formed:
  539 |       _Hashtable() = default;
      |       ^~~~~~~~~~
/usr/include/c++/14/bits/hashtable.h:539:7: error: use of deleted function 'std::__detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _Traits>::_Hashtable_base() [with _Key = std::pair<long long int, long long int>; _Value = std::pair<const std::pair<long long int, long long int>, long long int>; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long long int, long long int> >; _Hash = std::hash<std::pair<long long int, long long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _Traits = std::__detail::_Hashtable_traits<true, false, true>]'
In file included from /usr/include/c++/14/bits/hashtable.h:35:
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: note: 'std::__detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _Traits>::_Hashtable_base() [with _Key = std::pair<long long int, long long int>; _Value = std::pair<const std::pair<long long int, long long int>, long long int>; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long long int, long long int> >; _Hash = std::hash<std::pair<long long int, long long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _Traits = std::__detail::_Hashtable_traits<true, false, true>]' is implicitly deleted because the default definition would be ill-formed:
 1731 |       _Hashtable_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: error: use of deleted function 'std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _Hash, _RangeHash, _Unused, __cache_hash_code>::_Hash_code_base() [with _Key = std::pair<long long int, long long int>; _Value = std::pair<const std::pair<long long int, long long int>, long long int>; _ExtractKey = std::__detail::_Select1st; _Hash = std::hash<std::pair<long long int, long long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; bool __cache_hash_code = true]'
/usr/include/c++/14/bits/hashtable_policy.h: In instantiation of 'std::__detail::_Hashtable_ebo_helper<_Nm, _Tp, true>::_Hashtable_ebo_helper() [with int _Nm = 1; _Tp = std::hash<std::pair<long long int, long long int> >]':
/usr/include/c++/14/bits/hashtable_policy.h:1328:7:   required from here
 1328 |       _Hash_code_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1245:49: error: use of deleted function 'std::hash<std::pair<long long int, long long int> >::hash()'
 1245 |       _Hashtable_ebo_helper() noexcept(noexcept(_Tp())) : _Tp() { }
      |                                                 ^~~~~
In file included from /usr/include/c++/14/string_view:50,
                 from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/functional_hash.h:102:12: note: 'std::hash<std::pair<long long int, long long int> >::hash()' is implicitly deleted because the default definition would be ill-formed:
  102 |     struct hash : __hash_enum<_Tp>
      |            ^~~~
/usr/include/c++/14/bits/functional_hash.h:102:12: error: no matching function for call to 'std::__hash_enum<std::pair<long long int, long long int>, false>::__hash_enum()'
/usr/include/c++/14/bits/functional_hash.h:83:7: note: candidate: 'std::__hash_enum<_Tp, <anonymous> >::__hash_enum(std::__hash_enum<_Tp, <anonymous> >&&) [with _Tp = std::pair<long long int, long long int>; bool <anonymous> = false]'
   83 |       __hash_enum(__hash_enum&&);
      |       ^~~~~~~~~~~
/usr/include/c++/14/bits/functional_hash.h:83:7: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/14/bits/functional_hash.h:102:12: error: 'std::__hash_enum<_Tp, <anonymous> >::~__hash_enum() [with _Tp = std::pair<long long int, long long int>; bool <anonymous> = false]' is private within this context
  102 |     struct hash : __hash_enum<_Tp>
      |            ^~~~
/usr/include/c++/14/bits/functional_hash.h:84:7: note: declared private here
   84 |       ~__hash_enum();
      |       ^
/usr/include/c++/14/bits/hashtable_policy.h:1245:49: note: use '-fdiagnostics-all-candidates' to display considered candidates
 1245 |       _Hashtable_ebo_helper() noexcept(noexcept(_Tp())) : _Tp() { }
      |                                                 ^~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1328:7: note: 'std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _Hash, _RangeHash, _Unused, __cache_hash_code>::_Hash_code_base() [with _Key = std::pair<long long int, long long int>; _Value = std::pair<const std::pair<long long int, long long int>, long long int>; _ExtractKey = std::__detail::_Select1st; _Hash = std::hash<std::pair<long long int, long long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; bool __cache_hash_code = true]' is implicitly deleted because the default definition would be ill-formed:
 1328 |       _Hash_code_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1328:7: error: use of deleted function 'std::__detail::_Hashtable_ebo_helper<1, std::hash<std::pair<long long int, long long int> >, true>::~_Hashtable_ebo_helper()'
/usr/include/c++/14/bits/hashtable_policy.h:1242:12: note: 'std::__detail::_Hashtable_ebo_helper<1, std::hash<std::pair<long long int, long long int> >, true>::~_Hashtable_ebo_helper()' is implicitly deleted because the default definition would be ill-formed:
 1242 |     struct _Hashtable_ebo_helper<_Nm, _Tp, true>
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1242:12: error: use of deleted function 'std::hash<std::pair<long long int, long long int> >::~hash()'
/usr/include/c++/14/bits/functional_hash.h:102:12: note: 'std::hash<std::pair<long long int, long long int> >::~hash()' is implicitly deleted because the default definition would be ill-formed:
  102 |     struct hash : __hash_enum<_Tp>
      |            ^~~~
/usr/include/c++/14/bits/functional_hash.h:102:12: error: 'std::__hash_enum<_Tp, <anonymous> >::~__hash_enum() [with _Tp = std::pair<long long int, long long int>; bool <anonymous> = false]' is private within this context
/usr/include/c++/14/bits/functional_hash.h:84:7: note: declared private here
   84 |       ~__hash_enum();
      |       ^
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: note: use '-fdiagnostics-all-candidates' to display considered candidates
 1731 |       _Hashtable_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: error: use of deleted function 'std::__detail::_Hash_code_base<std::pair<long long int, long long int>, std::pair<const std::pair<long long int, long