蓝桥杯备考-----＞DFS组合型枚举，选数问题

#include <iostream>
using namespace std;
int n, k;
const int N = 25;
int a[N];
int path;
int ret;

bool isprime(int x)
{
	if (x <= 1) return false;
	else
	{
		for (int i = 2; i <= x / i; i++)
		{
			if (x % i == 0)
			{
				return false;
			}
		}
	}
	return true;
}
void dfs(int pos, int begin)
{
	if (pos > k)
	{
		if (isprime(path))
			ret++;
		return;
	}
	for (int i = begin; i <= n; i++)
	{
		path += a[i];
		dfs(pos + 1, i + 1);
		path -= a[i];
	}
}
int main()
{
	cin >> n >> k;

	for (int i = 1; i <= n; i++)
	{
		cin >> a[i];
	}

	dfs(1, 1);

	cout << ret << endl;





	return 0;
}