[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[],num[];
 int main(){
     int t;
     cin>>t;
     while(t--){
         memset(num,,sizeof num);
         int n;
         cin>>n;
         for(int i=;i<n;i++){
             cin>>a[i];
         }
         for(int i=;i<n;i++){
             num[a[i]]++;
         }
         int sum=;
         for(int i=;i<=;i++){
             if(num[i]>=) sum+=i*(pow(,n)-pow(,n-num[i]));
         }
         cout<<sum<<endl;
     }
 }