dfs hdu 1016

http://acm.hdu.edu.cn/showproblem.php?pid=1016

#include <cstdio>#include <cstring>using namespace std;int prime[40]={0};int n,count;int ans[21];int vis[21];void dfs(int x){    if(count==n&&!prime[ans[0]+ans[n-1]])    {        printf("%d",ans[0]);        for(int i = 1; i<n; i++)            printf(" %d",ans[i]);        printf("\n");    }    for(int i = 2; i<=n; i++)        if(!prime[x+i]&&!vis[i])        {            vis[i]=1;            ans[count++]=i;            dfs(i);            count--;            vis[i]=0;        }}int main(){    for(int i = 2; i<40; i++)        if(!prime[i])            for(int j = i+i; j<40; j+=i)                prime[j]=1;    int k = 1;    while(scanf("%d",&n)!=EOF)    {        count=1;        memset(vis,0,sizeof(vis));        ans[0]=1;        printf("Case %d:\n",k);        dfs(1);        printf("\n");        k++;    }}