RT,先上代码

#include <bits/stdc++.h>

using namespace std;


int book[15000001] = {0}, pri[15000001] = {0}, ori[21] = {0}, sum = 0, counts = 0;

void booking(int, int);
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	int n, k;
	cin >> n >> k;
	
	//ori记录原始数据 
	for(int i = 0; i < n; i ++) cin >> ori[i];
	
	// 埃氏筛法筛选质数 
	pri[0] = pri[1] = 1; // 0标记质数 
	for(int i = 2; i*i <= 15000001; i ++)
	{
		if(pri[i] == 0)
			for(int j = 2; i*j <= 15000001; j ++) pri[i*j] = 1;		
	}
	
	//标记出现过的k个数的和,共有n个数 
	booking(k, n);
	
	cout << counts;
		
	return 0;
}

void booking(int num, int lim)
{
	if(num == 0)
	{
		if(book[sum] == 0 && pri[sum] == 0) counts ++;
		book[sum] = 1;// book标记已选过 
		return;
	}
	
	// i从num-1开始,因为之后还有num-1个数待选; 
	// 因为不要求顺序,所以枚举范围缩小到lim 
	for(int i = num-1; i < lim; i ++)
	{ 
		sum += ori[i];
		booking(num-1, i);
		sum -= ori[i];
	}
	return;
}

正确的是#2和#5,没找到哪里有问题...