Language: C++

// Active Infants 動的計画法　ソート
#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0;i<(n);i++)

int main(){
    int N;
    cin>>N;
    vector<long long> a(N);
    rep(i,N){
        cin>>a[i];
    }
 	vector<int> index(a.size());
	iota(index.begin(), index.end(), 0); // indexに0から順に代入
	sort(
        index.begin(),
        index.end(),
        [&](int x, int y){return a[x] > a[y];} // 降順
	);
    // a[]の順番は変わらない
 //   cout<<endl;
 //   rep(i,N){
 //       cout<<a[i]<<" "<<index[i]<<endl;
 //   }
    long long DP[N][N]={};
    DP[0][0]=0;
    int k;
    for(int i=1;i<=N;i++){
        for(int j=0;j<(i+1);j++){
            k=i-j;
            if(j>0 && k>0){
                if(DP[j-1][k]+a[index[i-1]]*(index[i-1]-(j-1))>DP[j][k-1]+a[index[i-1]]*((N-k)-index[i-1])){
                    DP[j][k]=DP[j-1][k]+a[index[i-1]]*(index[i-1]-(j-1));
                }
                else{
                    DP[j][k]=DP[j][k-1]+a[index[i-1]]*((N-k)-index[i-1]);
                }
            } 
            else if(j>0) {
                DP[j][k]=DP[j-1][k]+a[index[i-1]]*(index[i-1]-(j-1));
            }
            else {
                DP[j][k]=DP[j][k-1]+a[index[i-1]]*((N-k)-index[i-1]);
            }
 //           cout<<j<<" "<<k<<" "<<DP[j][k]<<endl;
        }
    }
 //   cout<<endl;
    long ans=0;
    rep(i,N){
        int j=N-i;
        ans=max(ans, DP[i][j]);
    }
    cout<<ans<<endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:53:16: error: no matching function for call to 'max(long int&, long long int&)'
   53 |         ans=max(ans, DP[i][j]);
      |             ~~~^~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:53:16: note:   deduced conflicting types for parameter 'const _Tp' ('long int' and 'long long int')
   53 |         ans=max(ans, DP[i][j]);
      |             ~~~^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:53:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long int'
   53 |         ans=max(ans, DP[i][j]);
      |             ~~~^~~~~~~~~~~~~~~