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hdu 1016 Prime Ring Problem(dfs)
Prime Ring Problem
Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 28391 Accepted Submission(s): 12644
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.
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.
You are to write a program that completes above process.
Print a blank line after each case.
Sample Input
68
Sample Output
Case 1:1 4 3 2 5 61 6 5 2 3 4Case 2:1 2 3 8 5 6 7 41 2 5 8 3 4 7 61 4 7 6 5 8 3 21 6 7 4 3 8 5 2
重新做了一遍素数环 没想到还是出了点小问题
从第一个数开始dfs 按字典序把符合条件的数计入seq数组
再通过回溯 把所有的情况都遍历并输出
(n==1的情况数据中不会出现 判不判断都可以)
#include<cmath>#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespace std;int n;int vis[50];int seq[50];int prime[100];bool okp(int x){ int i; for(i=2;i<=sqrt(x);i++) { if(x%i==0) break; } if(i>sqrt(x)) return true; return false;}void prim(){ memset(prime,0,sizeof(prime)); int i; for(i=2;i<=50;i++) { if(prime[i]==0) { if(okp(i)) prime[i]=1; } int k=i,tc=2; while(k*tc<=50) { prime[k*tc]=2; tc++; } }}void dfs(int x){ int i; if(x>n) return ; if(x==n&&prime[seq[x]+1]==1) { for(i=1;i<=n;i++) { printf("%d",seq[i]); printf("%c",i==n?‘\n‘:‘ ‘); } } else { for(i=2;i<=n;i++) { if(vis[i]==0&&prime[seq[x]+i]==1) { vis[i]=1; seq[x+1]=i; dfs(x+1); vis[i]=0; } } }}int main(){ int cas=1,i,j; prim();//筛法求素数 while(scanf("%d",&n)!=EOF) { printf("Case %d:\n",cas++); //if(n==1) continue; //测试数据中不会出现n==1 memset(vis,0,sizeof(vis)); seq[1]=1; vis[1]=1; dfs(1); printf("\n"); } return 0;}
hdu 1016 Prime Ring Problem(dfs)
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