回溯素数环

回溯实现素数环

import java.util.*;
public class Prime {
  public  static  void  main(String arg[])
  {
       int t,i,j,k,s,n,count=0;
       int[] a=new int[2000];
       int[] b=new int[1000];
       Scanner input=new Scanner(System.in);
       n=input.nextInt();
       for(k=1;k<=2*n;k++) b[k]=0;
       for(k=3;k<=2*n;k+=2){
           for(t=0,j=3;j<=Math.sqrt(k);j+=2)
              if(k%j==0){
                  t=1;break;
              }
           if(t==0) b[k]=1;  
       }
       System.out.println("8项素数和环：");
       a[1]=1;s=0;
       i=2;a[i]=2;
       while(true){
           t=1;
           count++;
           for(j=1;j<i;j++)
               if(a[j]==a[i]||b[a[i]+a[i-1]]!=1){
                   t=0;break;
               }
           if(t==1&&i==n&&b[a[n]+1]==1){
               s++;
               System.out.print(s+":1");
               for(j=2;j<=n;j++)
                   System.out.print(","+a[j]);
               System.out.println("");
           }
           if(t==1&&i<n)
           {i++;a[i]=2;continue;}
           while(a[i]==n&&i>1) i--;
           if(i>1) a[i]++;
           else break;
       }
System.out.println("循环次数"+count);
  }
}