zoj1457_Prime Ring Problem

 

     用了dfs非递归，略感复杂，用时居然400多MS，悲催。

    

     #include<iostream>#include<stdio.h>#include<math.h>using namespace std;#define MAX 21int mark[MAX];int judge[MAX][MAX];int stack[1000];int n;bool prime(int x){if(x==2||x==3 ||x==5||x==7||x==11||x==13||x==17||x==19||x==23||x==29 ||x==31 || x==37)return true;elsereturn false;}void setjudge(){int i,j;int sum;for(i=1;i<20;i++)for(j=i+1;j<=20;j++){sum=i+j;if(prime(sum)){judge[i][j]=1;judge[j][i]=1;}}}void dfs(){int top=-1;int cur,i,pos=1,j;int flag;stack[++top]=1;mark[1]=1;while(top>-1){flag=0;cur=stack[top];while(!flag){flag=1;for(i=pos+1;i<=n;i++){if(!mark[i] && judge[cur][i]){flag=0;mark[i]=1;stack[++top]=i;cur=i;pos=1;break;}}}if(top==n-1 && judge[stack[top]][1]){for(j=0;j<n-1;j++)printf("%d ",stack[j]);printf("%d/n",stack[j]);}pos=stack[top];mark[pos]=0;top--;}}int main(){int t=1;setjudge();while(cin>>n){cout<<"Case "<<t++<<":"<<endl;if(n%2==0)dfs();cout<<endl;}return 0;}