Language: C++

#include<bits/stdc++.h>


using namespace std;

int main(){
  cin.tie(0);
  ios::sync_with_stdio(0);
  string a, b;
  int n;
  cin >> n;
  int c[26];
  for(int i = 0; i < 26; i++){
    c[i] = 1 << 25;
  }
  for(int i = 0; i < n; i++){
    string str;
    cin >> str;
    sort(str.begin(), str.end());
    for(int j = 0; j < 26; j++){
      c[j] = min(c[j], upper_bound(str.begin(), str.end(), j + 'a') - lower_bound(str.begin(), str.end(), j + 'a'));
    }
  }
  for(int i = 0; i < 26; i++){
    while(c[i]--)
      cout << char(i + 'a');
  }
  cout << "\n";
}

Compiler output:
a.cc: In function 'int main()':
a.cc:21:17: error: no matching function for call to 'min(int&, __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >::difference_type)'
   21 |       c[j] = min(c[j], upper_bound(str.begin(), str.end(), j + 'a') - lower_bound(str.begin(), str.end(), j + 'a'));
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:21:17: note:   deduced conflicting types for parameter 'const _Tp' ('int' and '__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >::difference_type' {aka 'long int'})
   21 |       c[j] = min(c[j], upper_bound(str.begin(), str.end(), j + 'a') - lower_bound(str.begin(), str.end(), j + 'a'));
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5696:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::min(initializer_list<_Tp>, _Compare)'
 5696 |     min(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5696:5: note:   template argument deduction/substitution failed:
a.cc:21:17: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   21 |       c[j] = min(c[j], upper_bound(str.begin(), str.end(), j + 'a') - lower_bound(str.begin(), str.end(), j + 'a'));
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~