So easy

Code:

#include<bits/stdc++.h>
using namespace std;
const int N = 100001;
int n;
double sum1 = 0, sum2 = 0;
struct stu {
	double t;
	int id;
} a[N];
bool cmp(stu aa, stu bb) {
	return aa.t < bb.t;
}
int main() {
	cin >> n;
	for (int i = 1; i <= n; ++i) {
		cin >> a[i].t;
		a[i].id = i;
	}
	sort(a + 1, a + 1 + n, cmp);
	for (int i = 1; i <= n; ++i)
		cout << a[i].id << " ";
	cout << endl;
	for (int i = 1; i < n; i++) {
		sum1 = sum1 + a[i].t;
		sum2 = sum2 + sum1;
	}
	cout << fixed << setprecision(2) << sum2 * 1.0 / n;
	return 0;
}

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