Language: C++

#include <iostream>
#include <vector>
typedef long long ll
using namespace std;

int main(){
  int n;
  cin >> n;
  string str;
  cin >> str;
  ll sum = 0;
  vector<int> vec(26, 0);
  for(int i=0; i<n; i++){
    vec[str[i]-'a']++;
    ll mul = 1;
    for(int j=0; j<26; j++){
      if(j==str[i]-'a') continue;
      mul *= vec[j]+1;
      mul %= 1000000007;
    }
    sum += mul;
    sum %= 1000000007;
  }
  cout << sum << endl;
  return 0;
}
      

Compiler output:
a.cc:4:1: error: expected initializer before 'using'
    4 | using namespace std;
      | ^~~~~
a.cc: In function 'int main()':
a.cc:8:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    8 |   cin >> n;
      |   ^~~
      |   std::cin
In file included from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:9:3: error: 'string' was not declared in this scope
    9 |   string str;
      |   ^~~~~~
a.cc:9:3: note: suggested alternatives:
In file included from /usr/include/c++/14/iosfwd:41,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
In file included 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:
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:10:10: error: 'str' was not declared in this scope; did you mean 'std'?
   10 |   cin >> str;
      |          ^~~
      |          std
a.cc:11:3: error: 'll' was not declared in this scope
   11 |   ll sum = 0;
      |   ^~
a.cc:12:3: error: 'vector' was not declared in this scope
   12 |   vector<int> vec(26, 0);
      |   ^~~~~~
a.cc:12:3: note: suggested alternatives:
In file included from /usr/include/c++/14/vector:66,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_vector.h:428:11: note:   'std::vector'
  428 |     class vector : protected _Vector_base<_Tp, _Alloc>
      |           ^~~~~~
/usr/include/c++/14/vector:93:13: note:   'std::pmr::vector'
   93 |       using vector = std::vector<_Tp, polymorphic_allocator<_Tp>>;
      |             ^~~~~~
a.cc:12:10: error: expected primary-expression before 'int'
   12 |   vector<int> vec(26, 0);
      |          ^~~
a.cc:14:5: error: 'vec' was not declared in this scope
   14 |     vec[str[i]-'a']++;
      |     ^~~
a.cc:15:7: error: expected ';' before 'mul'
   15 |     ll mul = 1;
      |       ^~~~
      |       ;
a.cc:18:7: error: 'mul' was not declared in this scope
   18 |       mul *= vec[j]+1;
      |       ^~~
a.cc:21:5: error: 'sum' was not declared in this scope
   21 |     sum += mul;
      |     ^~~
a.cc:21:12: error: 'mul' was not declared in this scope
   21 |     sum += mul;
      |            ^~~
a.cc:24:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   24 |   cout << sum << endl;
      |   ^~~~
      |   std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:24:11: error: 'sum' was not declared in this scope
   24 |   cout << sum << endl;
      |           ^~~
a.cc:24:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   24 |   cout << sum << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~