ZOJ 1457 Prime Ring Problem(dfs+剪枝)
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
#include<iostream> #include<cstdio> #include<cstring> #include<cmath> using namespace std; int n,test=0;; int cir[30]; int vis[30]; int prime[50]={0}; void dfs(int k) { if(k==n) { if(!prime[cir[k]+cir[1]]) return; for(int i=1;i<n;i++) printf("%d ",cir[i]); printf("%d",cir[n]); printf("\n"); return; } for(int j=2;j<=n;j++) { if(!vis[j]&&prime[cir[k]+j]) //对于相邻素数的推断,在这里才干在zoj,AC,放最前面就仅仅能在HDU,AC了,一层递归调用的时间而已啊! { vis[j]=1; cir[k+1]=j; dfs(k+1); vis[j]=0; //注意递归复原,这预计是最大的亮点了 } } } int main() { prime[3]=1; prime[5]=1; prime[7]=1; prime[11]=1; prime[13]=1; prime[17]=1; prime[19]=1; prime[23]=1; prime[29]=1; prime[31]=1; prime[37]=1; while(scanf("%d",&n)!=EOF) { //memset(cir,0,sizeof cir); //memset(vis,0,sizeof vis); for(int i=1;i<=n;i++) { vis[i]=0; } printf("Case %d:\n",++test); if(n % 2 == 1) { printf("\n"); continue; } cir[1]=1; dfs(1); printf("\n"); } return 0; }
posted on 2017-08-18 16:03 gavanwanggw 阅读(214) 评论(0) 编辑 收藏 举报