HDU 1016 Prime Ring Problem(単純遡及)
Problem B
Time Limit : 4000/2000ms (Java/Other) Memory Limit : 65536/32768K (Java/Other)
Total Submission(s) : 11 Accepted Submission(s) : 8
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. [img]../../data/images/1016-1.gif[/img]
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
Sample Output
Time Limit : 4000/2000ms (Java/Other) Memory Limit : 65536/32768K (Java/Other)
Total Submission(s) : 11 Accepted Submission(s) : 8
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. [img]../../data/images/1016-1.gif[/img]
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
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;
const int MAXN=25;
int f[MAXN];
bool done[MAXN];
int csc=0;
int is_prim(int x)
{
int i;
int k=sqrt(x);
for(i=2;i<=k;i++)
if(x%i==0)break;
if(i>k)return 1;
return 0;
}
void select(int n,int cur)
{
int i;
if(cur==n+1&&is_prim(f[1]+f[n]))
{
for(i=1;i<=n;i++)
if(i!=n)printf("%d ",f[i]);
else printf("%d
",f[i]);
}
if(cur==n+1) return;
for(i=1;i<=n;i++)
{
if(!done[i]&&is_prim(f[cur-1]+i))
{
f[cur]=i;
done[i]=1;
select(n,cur+1);
done[i]=0;
}
}
}
int main()
{
// freopen("123.txt","r",stdin);
int n,i;
while(~scanf("%d",&n))
{
printf("Case %d:
",++csc);
memset(done,0,sizeof(done));
f[1]=1;
done[1]=1;
select(n,2);
done[1]=0;
printf("
");
}
return 0;
}