Language: C++

#include<iostream>
#include<algorithm>
#include<vector>
#include<string>


int main() {

	int n = 0;
	std::cin >> n;
	std::vector<std::string>str(n);
	std::vector<std::pair<char, int>>str_char_pair{};

	bool enable = false;
	for (int i = 0; i < n; i++)
	{
		std::cin >> str[i];
		for (char c = 'a'; c <= 'z'; c++)
		{
			int count = std::count(str[i].begin(), str[i].end(), c);

			if (count >= 1) {
				str_char_pair.emplace_back(c, count);
			}
		}
	}
	std::sort(str_char_pair.begin(), str_char_pair.end());
	std::vector<std::pair<char, int>>enable_str_pair;
	for (char c = 'a'; c <= 'z'; c++)
	{
		int count = std::count_if(str_char_pair.begin(), str_char_pair.end(), [&c](std::pair<char, int>p) ->bool {return p.first == c;});
		if (count == n)
		{
			auto it = std::find(str_char_pair.begin(), str_char_pair.end(), [&c](std::pair<char, int>p) ->bool {return p.first == c;});
			/*auto it = str_char_pair.begin();
			for (auto i = str_char_pair.begin(); i != str_char_pair.end(); i++)
			{
				bool b = [&c](std::pair<char, int>p) ->bool {return p.first == c;}(*i);
				if (b) {
					it = i;
					break;
				}
			}*/

			for (size_t i = 0; i < n; i++)
			{
				enable_str_pair.push_back(*(it + i));
			}
		}
	}

	for (char c = 'a'; c <= 'z'; c++)
	{
		for (auto& i : enable_str_pair)
		{
			if (i.first == c)
			{
				for (int j = 0; j < i.second; j++)
				{
					std::cout << c;
					enable = true;
				}
				break;
			}
		}
	}
	if (!enable)std::cout << "";
	std::cout << std::endl;
}


Compiler output:
In file included from /usr/include/c++/14/bits/stl_algobase.h:71,
                 from /usr/include/c++/14/string:51,
                 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/predefined_ops.h: In instantiation of 'bool __gnu_cxx::__ops::_Iter_equals_val<_Value>::operator()(_Iterator) [with _Iterator = __gnu_cxx::__normal_iterator<std::pair<char, int>*, std::vector<std::pair<char, int> > >; _Value = const main()::<lambda(std::pair<char, int>)>]':
/usr/include/c++/14/bits/stl_algobase.h:2107:14:   required from '_RandomAccessIterator std::__find_if(_RandomAccessIterator, _RandomAccessIterator, _Predicate, random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<pair<char, int>*, vector<pair<char, int> > >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val<const main()::<lambda(pair<char, int>)> >]'
 2107 |           if (__pred(__first))
      |               ~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:2152:23:   required from '_Iterator std::__find_if(_Iterator, _Iterator, _Predicate) [with _Iterator = __gnu_cxx::__normal_iterator<pair<char, int>*, vector<pair<char, int> > >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val<const main()::<lambda(pair<char, int>)> >]'
 2152 |       return __find_if(__first, __last, __pred,
      |              ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
 2153 |                        std::__iterator_category(__first));
      |                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:3850:28:   required from '_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator<pair<char, int>*, vector<pair<char, int> > >; _Tp = main()::<lambda(pair<char, int>)>]'
 3850 |       return std::__find_if(__first, __last,
      |              ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
 3851 |                             __gnu_cxx::__ops::__iter_equals_val(__val));
      |                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:34:23:   required from here
   34 |                         auto it = std::find(str_char_pair.begin(), str_char_pair.end(), [&c](std::pair<char, int>p) ->bool {return p.first == c;});
      |                                   ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/predefined_ops.h:270:24: error: no match for 'operator==' (operand types are 'std::pair<char, int>' and 'const main()::<lambda(std::pair<char, int>)>')
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:1208:5: note: candidate: 'template<class _IteratorL, class _IteratorR, class _Container> bool __gnu_cxx::operator==(const __normal_iterator<_IteratorL, _Container>&, const __normal_iterator<_IteratorR, _Container>&)'
 1208 |     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1208:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const __gnu_cxx::__normal_iterator<_IteratorL, _Container>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1216:5: note: candidate: 'template<class _Iterator, class _Container> bool __gnu_cxx::operator==(const __normal_iterator<_Iterator, _Container>&, const __normal_iterator<_Iterator, _Container>&)'
 1216 |     operator==(const __normal_iterator<_Iterator, _Container>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1216:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const __gnu_cxx::__normal_iterator<_Iterator, _Container>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40:
/usr/include/c++/14/bits/postypes.h:192:5: note: candidate: 'template<class _StateT> bool std::operator==(const fpos<_StateT>&, const fpos<_StateT>&)'
  192 |     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:192:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const std::fpos<_StateT>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:235:5: note: candidate: 'template<class _T1, class _T2> bool std::operator==(const allocator<_CharT>&, const allocator<_T2>&)'
  235 |     operator==(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:235:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const std::allocator<_CharT>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const std::reverse_iterator<_Iterator>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const std::reverse_iterator<_Iterator>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const std::move_iterator<_IteratorL>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'const std::move_iterator<_IteratorL>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'const main()::<lambda(std::pair<char, int>)>' is not derived from 'const std::pair<_T1, _T2>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:629:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  629 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:629:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/string_view:637:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  637 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:637:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/predefined_ops.h:270:24: note:   'std::pair<char, int>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  270 |         { return *__it == _M_value; }
      |                  ~~~~~~^~~~~~~~~~~
/usr/include/c++/14/string_view:644:5: note: candidate: 'template<class _CharT, class _Trai