[xjtu21]wmq的午餐 计数问题

http://oj.xjtuacm.com/problem/21/

对13进行分析，每种价格出现的次数：

 $(C_m^1 + C_m^2 + ... + C_m^m)(C_{n - m}^0 + C_{n - m}^1 + C_{n - m}^2 + ... + C_{n - m}^{n - m}) = ({2^m} - 1)*{2^{n - m}} = {2^n} - {2^m}$

---

---

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<cmath>
using namespace std;
typedef long long ll;
int a[1000],num[20];
int main(){
    int t;
    cin>>t;
    while(t--){
        memset(num,0,sizeof num);
        int n;
        cin>>n;
        for(int i=0;i<n;i++){
            cin>>a[i];
        }
        for(int i=0;i<n;i++){
            num[a[i]]++;
        }
        int sum=0;
        for(int i=0;i<=13;i++){
            if(num[i]>=1) sum+=i*(pow(2,n)-pow(2,n-num[i]));
        }
        cout<<sum<<endl;
    }
}