CodeVS1008 选数 题解

#include <cstdio>#include <algorithm>using namespace std;int N, K;int num[20+2];bool flag[20+2];int ans[20+2];int cnt;bool cmp(int a, int b){    return a<b;}bool IsPrime(int n){    if(n<2) return false;    if(n==2 || n==3) return true;    if(n%2==0 || n%3==0) return false;    for(int i=5, d=4; i*i<=n; i+=d^=6){        if(n%i==0) return false;    }    return true;}void Array(int n, int p){    if(n>K){        int tmp = 0;        for(int i = 1; i<=K; ++i) tmp+=ans[i];        if(IsPrime(tmp)) ++cnt;        return;    }    for(int i = p; i<N; ++i){        if(!flag[i]){            flag[i] = true;            ans[n] = num[i];            Array(n+1, i);            flag[i] = false;        }    }}int main(){    scanf("%d %d", &N, &K);    for(int i = 0; i<N; ++i) scanf("%d", &num[i]);    sort(num, num+N, cmp);    Array(1, 0);    printf("%d\n", cnt);    return 0;}