Language: C++

#include <iostream>
#include <vector>
#include <numeric>
#include <algorithm>


using namespace std;

int main(){
  size_t n{};
  cin >> n;
  vector<pair<size_t ,size_t>> ml{};
  vector<pair<size_t ,size_t>> mr{};
  for(size_t i = 0;i < n; i+=2){
    size_t l,r;
    cin >> l >> r;

    auto fl = find(ml.begin(),ml.end(),[&](auto p){ return p.first == l;});
    if(true){
      ml.emplace_back(l, 1);
    }else{
      //++fl->second;
    }

    auto fr = find(mr.begin(),mr.end(),[&](auto p){ return p.first == r;});
    if(true){
      mr.emplace_back(r, 1);
    }else{
      //++fr->second;
    }
  }
  
  if(ml.size() == 1 && mr.size() == 1){
    cout << ((ml.at(0).first != mr.at(0).first) ? 0 : (n / 2)) << endl;
  }else{
    size_t result = 0;

    if(ml.at(0).first != mr.at(0).first){
      if(ml.size() != 1){
        result += (n/2) - ml.at(0).second;
      }
      if(mr.size() != 1){
        result += (n/2) - mr.at(0).second;
      }
    }else{
      
    }

    cout << result << 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<long unsigned int, long unsigned int>*, std::vector<std::pair<long unsigned int, long unsigned int> > >; _Value = const main()::<lambda(auto:1)>]':
/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<long unsigned int, long unsigned int>*, vector<pair<long unsigned int, long unsigned int> > >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val<const main()::<lambda(auto:1)> >]'
 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<long unsigned int, long unsigned int>*, vector<pair<long unsigned int, long unsigned int> > >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val<const main()::<lambda(auto:1)> >]'
 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<long unsigned int, long unsigned int>*, vector<pair<long unsigned int, long unsigned int> > >; _Tp = main()::<lambda(auto:1)>]'
 3850 |       return std::__find_if(__first, __last,
      |              ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
 3851 |                             __gnu_cxx::__ops::__iter_equals_val(__val));
      |                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:18:19:   required from here
   18 |     auto fl = find(ml.begin(),ml.end(),[&](auto p){ return p.first == l;});
      |               ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/predefined_ops.h:270:24: error: no match for 'operator==' (operand types are 'std::pair<long unsigned int, long unsigned int>' and 'const main()::<lambda(auto:1)>')
  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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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<long unsigned int, long unsigned 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(auto:1)>' 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<long unsigned int, long unsigned 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: