题干：
Local authorities have heard a lot about combinatorial abilities of Ostap Bender so they decided to ask his help in the question of urbanization. There are n people who plan to move to the cities. The wealth of the i of them is equal to ai. Authorities plan to build two cities, first for n1 people and second for n2 people. Of course, each of n candidates can settle in only one of the cities. Thus, first some subset of candidates of size n1 settle in the first city and then some subset of size n2 is chosen among the remaining candidates and the move to the second city. All other candidates receive an official refuse and go back home.
To make the statistic of local region look better in the eyes of their bosses, local authorities decided to pick subsets of candidates in such a way that the sum of arithmetic mean of wealth of people in each of the cities is as large as possible. Arithmetic mean of wealth in one city is the sum of wealth ai among all its residents divided by the number of them (n1 or n2 depending on the city). The division should be done in real numbers without any rounding.
Please, help authorities find the optimal way to pick residents for two cities.
Input
The first line of the input contains three integers n, n1 and n2 (1 ≤ n, n1, n2 ≤ 100 000, n1 + n2 ≤ n) — the number of candidates who want to move to the cities, the planned number of residents of the first city and the planned number of residents of the second city.
The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 100 000), the i-th of them is equal to the wealth of the i-th candidate.
Output
Print one real value — the maximum possible sum of arithmetic means of wealth of cities' residents. You answer will be considered correct if its absolute or relative error does not exceed 10 - 6.
Namely: let's assume that your answer is a, and the answer of the jury is b. The checker program will consider your answer correct, if .
Examples
Input
2 1 1 1 5
Output
6.00000000
Input
4 2 1 1 4 2 3
Output
6.50000000
Note
In the first sample, one of the optimal solutions is to move candidate 1 to the first city and candidate 2 to the second.
In the second sample, the optimal solution is to pick candidates 3 and 4 for the first city, and candidate 2 for the second one. Thus we obtain (a3 + a4) / 2 + a2 = (3 + 2) / 2 + 4 = 6.5
题目大意：
给你n个数，在这n个数中取n1个数和n2个数，求出平均值a1，a2，使他们的平均值和最大。
解题报告：
假设n1城市的人少，n2城市的人数多，最富的人去n1，剩下的填满n2即可，注意用longlong，，好坑这一点，又忘开longlong了。
AC代码：
#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int MAX = 1e5 + 5 ;
ll n,n1,n2,tmp;
int a[MAX];
bool cmp(ll a,ll b) {return a > b;
}
int main()
{cin>>n>>n1>>n2;for(int i = 1; i<=n; i++) {cin>>a[i];}sort(a+1,a+n+1,cmp);if(n1 > n2) swap(n1,n2);for(int i = 1; i<=n1; i++) {tmp += a[i];}double ans = tmp * 1.0 / n1;tmp = 0;for(int i = n1+1; i<=n1 + n2; i++) {tmp += a[i];}ans += tmp*1.0/n2;printf("%.6f\n",ans);return 0 ;
}
)
