//java双端队列
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int a = in.nextInt();
            Deque<Integer> deque = new LinkedList<>();
            for(int i=0;i<a;i++) deque.offerLast(in.nextInt());
            System.out.println(caculate(deque));
        }
    }
    public static int caculate(Deque<Integer> deque){
        int sum = 0,day = 1;
        while(!deque.isEmpty()){
            if(deque.peekFirst() < deque.peekLast()){
                sum += day * deque.pollFirst();
                day ++;
            }else{
                sum += day * deque.pollLast();
                day ++;
            }
        }
        return sum;
    }
}

双指针（JAVA）

用两个指针指向头尾，每次都取较小值加上去。因为要获得最大值而且每次只能操作头尾，所以较大的值放在后面计算肯定会取得最优解。

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] v = new int[n];
        for (int i = 0; i < n; i++) {
            v[i] = sc.nextInt();
        }
        int head = 0;
        int tail = n - 1;
        int sum = 0;
        int day = 1;
        while (head <= tail) {
            if (v[head] < v[tail]) {
                sum += day * v[head++];
            } else {
                sum += day * v[tail--];
            }
            day++;
        }
        System.out.println(sum);
    }
}