hdu 1016 Prime Ring Problem

 

http://acm.hdu.edu.cn/showproblem.php?pid=1016

 

题目大意：给你一个n，输出用1~n的数组成一个环，相邻两数之间的和为素数。

 

解题思路：DFS

 

#include <stdio.h>#include <string.h>#define N 41bool yes[N];/*n是否为素数，0是，1不是*/int p[N],Stack[N],s;int len,n;bool visited[N];/*素数打表记录*/void GetPrime(){int i,j;for (i=2;i<N;i++){if(yes[i])continue;p[len++] = i;for(j=i*i;j<N;j+=i)if(!yes[j])yes[j] = 1;}}void DFS(int x,int count){int i;if (count==n&&!yes[x+1])/*结点已经全部找到*/{printf("1 ");for(i=0;i<s-1;i++)printf("%d ",Stack[i]);printf("%d/n",Stack[i]);return;}else{for (i=1;i<=n;i++){if (!visited[i]&&!yes[i+x]){visited[i] = 1;Stack[s++] = i;DFS(i,count+1);s--;/*出栈*/visited[i] = 0;/*退出下层递归，要还原状态*/}}}}int main(){int k = 1,i,count;memset(yes,0,sizeof(yes));GetPrime();while (scanf("%d",&n)!=EOF){printf("Case %d:/n",k++);count = 1;visited[1] = 1;for (i=2;i<=n;i++){if (!visited[i]&&!yes[i+1]){s = 0;Stack[s++] = i;visited[i] = 1;DFS(i,count+1);visited[i] = 0;s--;}}printf("/n");}return 0;}