HDU 1016 Prime Ring Problem

Prime Ring Problem

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 39784    Accepted Submission(s): 17541


Problem Description

A ring is compose of n circles as shown in diagram. Put natural number 1, 2, ..., n into each circle separately, and the sum of numbers in two adjacent circles should be a prime.

Note: the number of first circle should always be 1.



 

Input

n (0 < n < 20).

 

Output

The output format is shown as sample below. Each row represents a series of circle numbers in the ring beginning from 1 clockwisely and anticlockwisely. The order of numbers must satisfy the above requirements. Print solutions in lexicographical order.

You are to write a program that completes above process.

Print a blank line after each case.

 

Sample Input

6
8

 

Sample Output

Case 1:
1 4 3 2 5 6
1 6 5 2 3 4

Case 2:
1 2 3 8 5 6 7 4
1 2 5 8 3 4 7 6
1 4 7 6 5 8 3 2
1 6 7 4 3 8 5 2

 

题目大意：给定一个数字n,判断由1->n组成的圆环是否是素数圆环（每个数和周围的数字的和为素数）

#include <stdio.h>
#include <algorithm>
#include <string.h>
int a[30],b[30];
int n,num;
bool prime(int nn)
{
    if(nn==1)
        return 0;
    for(int i=2; i<nn; i++)
        if(nn%i==0)
        {
            return 0;
        }
    return 1;
}
void dfs(int s)
{
    if(s>n&&prime(a
+a[1]))
    {
        for(int i=1; i<n; i++)
        {
            printf("%d ",a[i]);
        }
        printf("%d\n",a
);
    }
    else
    {
        for (int i=2; i<=n; i++)
        {
            if(!b[i]&&prime(i+a[s-1]))
            {
                    b[i]=-1;
                    a[s]=i;
                    dfs(s+1);
                    b[i]=0;
            }
        }
    }
}
int main()
{
    num=0;
    while (scanf("%d",&n)!=EOF)
    {
        num++;
        printf("Case %d:\n",num);
        a[1]=1;
        b[1]=1;
        memset(b,0,sizeof(b));
        dfs(2);
        printf("\n");
    }
    return 0;
}

一开始把i定义为全局变量。。。。