Language: C++

#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
const int N = 1e5 + 10;

int main() {
    int n, k, a[51];
    cin >> n >> k;
    for(int i = 0; i < n; i++) {
        cin >> a[i];
    }
    int ans = 0;
    for(int i = 0; i <= 50; i++) {
        for(int j = 0; j <= 49; j++) {
            if(i + j > k || i + j > n) break;
            deque<int> v;
            for(int x = 0; x < i; x++) v.push_back(a[x]);
            for(int x = 0; x < j; x++) v.push_back(a[n-x-1]);
            sort(v.begin(), v.end());
            int res = 0;
            for(int x = 0; x < k-i-j && v.size() > 0; x++) {
                if(v.begin() < 0) v.pop_front();
            }
            for(int x = 0; x < v.size(); x++) {
                res += v[x];
            }
            ans = max(ans, res);
        }
    }
    cout << ans << endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:22:30: error: no match for 'operator<' (operand types are 'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} and 'int')
   22 |                 if(v.begin() < 0) v.pop_front();
      |                    ~~~~~~~~~ ^ ~
      |                           |    |
      |                           |    int
      |                           std::deque<int>::iterator {aka std::_Deque_base<int, std::allocator<int> >::iterator}
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:1143:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1143 |     operator<(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1143:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/regex.h:1224:5: 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>&)'
 1224 |     operator<(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1224:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/regex.h:1317:5: 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>&)'
 1317 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1317:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/regex.h:1391:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1391 |     operator<(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1391:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/regex.h:1485:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1485 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1485:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/regex.h:1560:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1560 |     operator<(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1560:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/regex.h:1660:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1660 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1660:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
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:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::pair<_T1, _T2>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::reverse_iterator<_Iterator>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::reverse_iterator<_Iterator>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::move_iterator<_IteratorL>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::deque<int>::iterator' {aka 'std::_Deque_base<int, std::allocator<int> >::iterator'} is not derived from 'const std::move_iterator<_IteratorL>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/string_view:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::_Deque_iterator<int, int&, int*>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:22:32: note:   'std::_Deque_iterator<int, int&, int*>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   22 |                 if(v.begin() < 0) v.pop_front();
      |                                ^
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> c