蓝桥杯备考：DFS之选数问题

#include <iostream>
#include <vector>
using namespace std;
int n,k;
const int N = 30;
int a[N];
int path,cnt;
bool isprime(int x)
{
	if(x<=1) return false;
	else
	{
		for(int i = 2;i<x;i++)
		{
			if(x%i == 0)
			return false;
		}
		return true;
	}
}
void dfs(int pos,int begin)
{
	if(pos>k)
	{
		if(isprime(path))
		cnt++;
		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 << cnt << endl;
	
	
	return 0;
}