WA了两个点，82分，不知道为什么。

#include<iostream>
#include<bits/stdc++.h>

using namespace std;

const int N = 1e3 + 10;
int n;
int a[N];
int back[N];
int ran[N];	//下标数组！ 
bool st[N];

int main ()
{
	cin >> n;

	for (int i=1; i <= n; i ++) {
		cin >> a[i];
		back[i] = a[i];
	}
	
	//排序：升序 
	sort (back+1, back+1+n);
	int k=1;
	for (int i=1; i <= n; i ++) {
		for (int j=1; j <= n; j ++) {
			if (back[i] == a[j] && !st[j]) {
				st[j] = true;
				ran[k ++] = j;
				break;
			}
		}
	}
	
	for (int i=1; i <= n; i ++) {
		cout << ran[i] << " ";
	}
	
	puts("");
	//计算总的等待时间： 
	int s=0;
	for (int i=1; i <= n; i ++) {
		s = s + back[i] * (n-i);
	}
	
	printf("%.2f", s *1.0/n);
	
	return 0;
}