Language: C++

#include <bits/stdc++.h>

#define ALL(a) (a).begin(), (a).end()
#define ll long long

using namespace std;

int tob(int x){
	int ret = 0;
	for(;x;x >>= 1)ret++;
	return ret;
}


signed main(){
	int n; cin >> n;
	vector<int> a(n);
	for(auto &e: a)cin >> e;
	int ans = 0;
	sort(ALL(a));
	for(auto itr = a.rbegin(); itr != a.rend(); ++itr){
		if(*itr == -1)break;
		int c = (1 << tob(*itr)) - *itr;
//		cerr << c << " ";
		auto lb = lower_bound(ALL(a), c);
		if(*lb == c && itr != lb){
			ans++;
			*lb = -1;
		}
	}
	cout << ans << endl;



	return 0;
}



Compiler output:
a.cc: In function 'int main()':
a.cc:26:36: error: no match for 'operator!=' (operand types are 'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   26 |                 if(*lb == c && itr != lb){
      |                                ~~~ ^~ ~~
      |                                |      |
      |                                |      __gnu_cxx::__normal_iterator<int*, std::vector<int> >
      |                                std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1132:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1132 |     operator!=(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1132:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:1212:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator!=(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1212 |     operator!=(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1212:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:1305:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1305 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1305:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:1379:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1379 |     operator!=(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1379:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:1473:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1473 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1473:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:1547:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1547 |     operator!=(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1547:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:1647:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1647 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1647:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/regex.h:2213:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator!=(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2213 |     operator!=(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2213:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1052:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator!=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1052 |     operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1052:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::pair<_T1, _T2>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:455:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  455 |     operator!=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:455:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' is not derived from 'const std::reverse_iterator<_Iterator>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  500 |     operator!=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' is not derived from 'const std::reverse_iterator<_IteratorR>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1686 |     operator!=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::move_iterator<_IteratorL>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1753 |     operator!=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::move_iterator<_IteratorL>'
   26 |                 if(*lb == c && itr != lb){
      |                                       ^~
In file included from /usr/include/c++/14/bits/char_traits.h:42,
                 from /usr/include/c++/14/string:42,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/postypes.h:197:5: note: candidate: 'template<class _StateT> bool std::operator!=(const fpos<_StateT>&, const fpos<_StateT>&)'
  197 |     operator!=(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:197:5: note:   template argument deduction/substitution failed:
a.cc:26:39: note:   'std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >' is not derived from 'const std::fpos<_StateT>'
   26 |                 if(*lb == c && itr !=