补充条件：m（arry存储）个里面选取n个。同时设置布尔数组（m个的）
以后统一设置前n个数组为1，用prev_permutation
例子：洛谷1249
#include<bits/stdc++.h>using namespace std;bool isnprimes[100000000];int primes[10000000];int cnt,sum;int count1;int k,n;void ola(int n){for(int i=2;i<=n;i++){if(isnprimes[i]==0)primes[++cnt]=i;for(int j=1;i*primes[j]<=n;j++){isnprimes[i*primes[j]]=1;if(i%primes[j]==0)break;}}}int main(){scanf("%d%d",&n,&k);int arry[n+1]={0};for(int i=1;i<=n;i++)scanf("%d",&arry[i]);int book[n+1]={0};for(int i=1;i<=k;i++)book[i]=1;ola(100000000);do{count1=0;for(int i=1;i<=n;i++){if(book[i]==1)count1+=arry[i];}if(isnprimes[count1]==0)sum++;}while(prev_permutation(book+1,book+1+n));printf("%d",sum);return 0;}
