Language: C++

#include<bits/stdc++.h>
using namespace std;
int main(){
  int n;
  cin >> n;
  map<string,long long int> m;
  while(n--){
    string str;
    cin >> str;
    sort(str.begin(),str.end());
    m[str]++;
  }
  long long int ans = 0;
for(int i = 0 ; i < m.size() ; i++)
  ans = ans + (m[i])*(m[i] - 1)/2;
  
    cout << ans << endl;  
  
}

Compiler output:
a.cc: In function 'int main()':
a.cc:15:17: error: no match for 'operator[]' (operand types are 'std::map<std::__cxx11::basic_string<char>, long long int>' and 'int')
   15 |   ans = ans + (m[i])*(m[i] - 1)/2;
      |                 ^
In file included from /usr/include/c++/14/map:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = std::__cxx11::basic_string<char>; _Tp = long long int; _Compare = std::less<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, long long int> >; mapped_type = long long int; key_type = std::__cxx11::basic_string<char>]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from 'int' to 'const std::map<std::__cxx11::basic_string<char>, long long int>::key_type&' {aka 'const std::__cxx11::basic_string<char>&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = std::__cxx11::basic_string<char>; _Tp = long long int; _Compare = std::less<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, long long int> >; mapped_type = long long int; key_type = std::__cxx11::basic_string<char>]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from 'int' to 'std::map<std::__cxx11::basic_string<char>, long long int>::key_type&&' {aka 'std::__cxx11::basic_string<char>&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~
a.cc:15:24: error: no match for 'operator[]' (operand types are 'std::map<std::__cxx11::basic_string<char>, long long int>' and 'int')
   15 |   ans = ans + (m[i])*(m[i] - 1)/2;
      |                        ^
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = std::__cxx11::basic_string<char>; _Tp = long long int; _Compare = std::less<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, long long int> >; mapped_type = long long int; key_type = std::__cxx11::basic_string<char>]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from 'int' to 'const std::map<std::__cxx11::basic_string<char>, long long int>::key_type&' {aka 'const std::__cxx11::basic_string<char>&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = std::__cxx11::basic_string<char>; _Tp = long long int; _Compare = std::less<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, long long int> >; mapped_type = long long int; key_type = std::__cxx11::basic_string<char>]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from 'int' to 'std::map<std::__cxx11::basic_string<char>, long long int>::key_type&&' {aka 'std::__cxx11::basic_string<char>&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~