hdu 1016 Prime Ring Problem（dfs）

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Prime Ring Problem

Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 28196 Accepted Submission(s): 12556

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

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
题目大意：给出一个小于20的数n，从1到n连成一个环，满足任意两个数之和都是素数 ，输出所有情况。思路：dfs深搜算法，刚开始接触，还是递归的使用，深度搜索。，不过Bfs也可以，正在学习2014,11,17
#include<stdio.h>#include<string.h>int v[23],b[23],n;int prime[]={1,0,0,0,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,1,1,0};void dfs(int x,int y){//dfs搜索算法 int i;if(y==n&&prime[b[n]+1]==0){printf("1");for(i=2;i<=n;i++)printf(" %d",b[i]);puts("");return;}else {for(i=2;i<=n;i++){if(prime[x+i]==0&&v[i]==0){b[y+1]=i;v[i]=1;dfs(i,y+1);//递归调用 v[i]=0;}}}}int main(){int k=1;while(scanf("%d",&n)==1){memset(b,0,sizeof(b));memset(v,0,sizeof(v));printf("Case %d:\n",k++);b[1]=1;//每组数都是从1开始 v[1]=1;dfs(1,1);puts("");}return 0;}

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