HDU Prime Ring Problem

#include<iostream>
#include<cstdio>
#include<cstring>
#define M 21
#define sc(x) scanf("%d",&x)
#define pf(x) printf("%d
",x)
#define PF(x) printf("%d ",x)
#define P printf("
")
#define CL(x,y) memset(x, y, sizeof(x))
#define FOR(i,x,v) for(int i=x; i<=v; i++)
using namespace std;
int prime[12]= {3,5,7,11,13,17,19,23,29,31,37};
int n, arr[M], used[M];
void DFS(int i);
bool check(int x);
void print();
int main()
{
    int k=1;
    while(~sc(n))
    {
        CL(arr, 0);
        CL(used, 0);
        printf("Case %d:
",k++);
        arr[1]=1;
        used[1]=1;
        DFS(2);
        P;
    }
    return 0;
}
bool check(int x)
{
    for(int k = 0; k < 11; k++)
        if(prime[k] == x)
            return true;
    return false;
}
void print()
{
    FOR(i, 1, n-1)//for(int i=1; i<n; i++)
    PF(arr[i]);
    pf(arr[n]);
}
void DFS(int i)
{
    if(i == n+1)
        print();
    else
    {
        FOR(j, 2, n)// for(int j = 2; j<= n; j++)
        {
            if(i == n)
            {
                if(!used[j] && check(j + arr[i-1]) && check(j + arr[1]))
                {
                    used[j] = 1;
                    arr[i] = j;
                    DFS(i+1);
                    used[j] = 0;
                }
            }
            else
            {
                if(!used[j] && check(j + arr[i-1]))
                {
                    used[j] = 1;
                    arr[i] = j;
                    DFS(i+1);
                    used[j] = 0;
                }
            }
        }
    }
}

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#define sc(x) scanf("%d",&x)
#define pf(x) printf("%d
",x)
#define PF(x) printf("%d",x)
#define CL(x,y) memset(x,y,sizeof(x))
using namespace std;
int prime[12]= {3,5,7,11,13,17,19,23,29,31,37};
const int MAX = 20;
int n;
int arr[MAX], used[MAX];
void DFS(int num);
bool check(int x);
int main()
{
    int k = 1;
    while(sc(n)!=EOF)
    {
        printf("Case %d:
", k++);
        CL(used, 0);
        CL(arr, 0);
        arr[1] = 1;
        used[1] = 1;
        DFS(2);
        cout << endl;
    }
    return 0;
}
void DFS(int num)
{
    if(num > n)
    {
        for(int i = 1; i <= n; i++)
        {
            printf("%d", arr[i]);
            if(i < n) printf(" ");
        }
        cout << endl;
    }
    else
        for(int j = 2; j <= n; j++)
        {
            if(num <= n-1)
            {
                if((arr[num-1]+j)&1 && !used[j] && check(arr[num-1]+j))
                {
                    used[j] = 1;
                    arr[num] = j;
                    DFS(num+1);
                    used[j] = 0;
                }
            }
            else
            {
                if((arr[num-1]+j)&1 && !used[j] && check(j+arr[1]) && check(arr[num-1]+j))
                {
                    used[j] = 1;
                    arr[num] = j;
                    DFS(num+1);
                    used[j] = 0;
                }
            }
        }
}
bool check(int x)
{
    int j;
    for(j = 3; j * j <= x; j++)
    {
        if(x % j == 0)
            return false;
    }
    return true;
}
//bool check(int x)
//{
//    for(int k = 0; k < 11; k++)
//        if(prime[k] == x)
//            return true;
//    return false;
//}