@[执笔、捃尘](/space/show?uid=18535) 有几种组合和为素数。
by 冈崎梦美 @ 2018-07-14 15:13:53
@[LGW2016B02](/space/show?uid=41953) 谢谢
by 4kilometers @ 2018-07-14 15:16:51
顺便帮改下吧
```cpp
#include<bits/stdc++.h>
using namespace std;
int n,k,tot=0;
long long a[21];
bool u[21];
void dfs (int,long long);
bool prime (long long);
int main()
{
scanf("%d%d",&n,&k);
for (int i=1;i<=n;++i) scanf("%I64d",&a[i]);
dfs(1,0);
printf("%d",tot);
return 0;
}
void dfs (int step,long long sum)
{
for (int i=1;i<=n;++i)
{
if (!u[i])
{
u[i]=true;
sum+=a[i];
if (step==k)
if (prime(sum))
tot++;
else dfs(step+1,sum);
u[i]=false;
sum-=a[i];
}
}
}
bool prime (long long x)
{
if (x==2||x==3) return true;
for (long long i=2;i<=sqrt(x);++i)
if (x%i==0) return false;
return true;
}
```
by 4kilometers @ 2018-07-14 15:23:40
err
by 詹自龚 @ 2018-07-14 15:39:00
@[王显然](/space/show?uid=86166) Orz
by 4kilometers @ 2018-07-14 15:44:44