Language: C++

#include <bits/stdc++.h>

using namespace std;

long long n, a[3010];
pair<long long, long long> memo[3010][3010];

pair<long long, long long> dp(long long l, long long r) {
	if(l > r) {
		return make_pair(0, 0);
	}
	if(memo[l][r] != make_pair(-1, -1)) {
		return memo[l][r];
	}
	memo[l][r] = make_pair(0, 0);
	if((n - (r - l + 1)) % 2 == 0) {
		pair<long long, long long> ret, temp;
		ret = make_pair(0, 0);
		temp = dp(l + 1, r);
		ret.first = ret.first + a[l] + temp.first;
		ret.second = ret.second + temp.second;
		memo[l][r] = ret;
		ret = make_pair(0, 0);
		temp = dp(l, r - 1);
		ret.first = ret.first + a[r] + temp.first;
		ret.second = ret.second + temp.second;
		if(ret.first - ret.second > memo[l][r].first - memo[l][r].second) {
			memo[l][r] = ret;
		}
	}
	else {
		pair<long long, long long> ret, temp;
		ret = make_pair(0, 0);
		temp = dp(l + 1, r);
		ret.first = ret.first + temp.first;
		ret.second = ret.second + a[l] + temp.second;
		memo[l][r] = ret;
		ret = make_pair(0, 0);
		temp = dp(l, r - 1);
		ret.first = ret.first + temp.first;
		ret.second = ret.second + a[r] + temp.second;
		if(ret.first - ret.second < memo[l][r].first - memo[l][r].second) {
			memo[l][r] = ret;
		}
	}
	return memo[l][r];
}

int main() {
	ios_base :: sync_with_stdio(false);
	cin.tie(NULL); cout.tie(NULL);
	for(long long i = 0; i < 3010; i++) {
		for(long long j = 0; j < 3010; j++) {
			memo[i][j] = make_pair(-1, -1);
		}
	}
	cin >> n;
	for(long long i = 1; i <= n; i++) {
		cin >> a[i];
	}
	pair<long long, long long> ans = dp(1, n);
	cout << ans.first - ans.second << endl;
}

Compiler output:
a.cc: In function 'std::pair<long long int, long long int> dp(long long int, long long int)':
a.cc:12:23: error: no match for 'operator!=' (operand types are 'std::pair<long long int, long long int>' and 'std::pair<int, int>')
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |            ~~~~~~~~~~ ^~ ~~~~~~~~~~~~~~~~~
      |                     |             |
      |                     |             pair<int,int>
      |                     pair<long long int,long long 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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<int, int>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<int, int>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
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:12:42: note:   deduced conflicting types for parameter '_T1' ('long long int' and 'int')
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::reverse_iterator<_Iterator>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::reverse_iterator<_Iterator>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::move_iterator<_IteratorL>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
/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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::move_iterator<_IteratorL>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
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:12:42: note:   'std::pair<long long int, long long int>' is not derived from 'const std::fpos<_StateT>'
   12 |         if(memo[l][r] != make_pair(-1, -1)) {
      |                                          ^
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:243:5: note: candidate: 'template<class _T1, class _T2> bool std::operator!=(const allocator<_CharT>&, const allocator<_T2>&)'
  243 |     operator!=(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:243:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::pair<long long int, long long int>' is not