[USACO 1.5.3]特殊的质数肋骨

题目：http://www.acmore.net/problem.php?cid=1013&pid=5

#include <iostream>
#include <stdio.h>
#include <string>
#include <string.h>
#include <algorithm>
#include <math.h>
#include <fstream>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <math.h>
#include <stdlib.h>
using namespace std ;
const int maxn=10008;
int prime[maxn];
int isprime[maxn];
int id,a_id;
int ans[maxn];
void make_prime(){
    memset(isprime,0,sizeof(isprime));
    id = 0;
    for(int i = 2;i < maxn;i++){
        if(!isprime[i])
            prime[id++] = i;
        for(int j = i+i;j < maxn;j+=i)
            if(!isprime[j])
                isprime[j] = 1;
    }
    //for(int i = 0;i < 1000;i++)
      //  printf("%d ",prime[i]);
}
bool check_isprime(int x){
    int temp = sqrt(x+0.5);
    for(int i = 0;i < id&&prime[i]<=temp;i++){
        if(x%prime[i] == 0)
            return 0;
    }
    return 1;
}
struct node{
    int num;
    int len;
    node(){}
    node(int n,int l):num(n),len(l){};
};
void bfs(int len){
    queue<node>que;
    que.push(node(2,1));
    que.push(node(3,1));
    que.push(node(5,1));
    que.push(node(7,1));
    while(!que.empty()){
        int temp,next;
        node now = que.front();
        que.pop();
        if(now.len == len){
            ans[a_id++] = now.num;
        }
        else{
            for(int i = 1;i < 10;i++){
                next = 10*now.num + i;
                if(check_isprime(next))
                    que.push(node(next,now.len+1));
            }
        }
    }
}
int main(){
    int n;
    while(~scanf("%d",&n)){
        make_prime();
        a_id = 0;
        bfs(n);
        for(int i = 0;i < a_id;i++)
            printf("%d\n",ans[i]);
    }
    return 0 ;
}