#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 1000006;
ll n;
struct node{
    ll www;
    ll num;
}a[N];
bool cmp(node c, node d){
    if(c.www == d.www) return c.num < d.num;
    return c.www < d.www;
}
int main(){
    cin >> n;
    for(int i = 1; i <= n; i++){
        cin >> a[i].www;
        a[i].num = i;
    }
    sort(a + 1, a + n + 1, cmp);
    for(int i = 1; i <= n; i++){
        cout << a[i].num << " ";
    }
    cout << endl;
    double sum = 0;
    ll pos = 1;
    for(int i = 1; i <= n; i++){
        sum += i * a[n - i].www;
    }
    printf("%.2lf", sum / n);
    return 0;
}

有没有大佬帮我解释一下 sum += i * a[n - i].www; 这个公式