pat（B）1007. 素数对猜想（素数打表）

代码：

#include<iostream>#include<cstdio>#include<cstring>using namespace std;int p[100005];int prime(int n){if(n==2||n==3)return 1;if(n%6!=1&&n%6!=5)return 0;for(int i=5;i*i<=n;i+=6){if(n%i==0||n%(i+2)==0)return 0;}return 1;}int main(){    int n;int k=0,j;for(j=2;j<100005;j++){if(prime(j))p[++k]=j;}while(scanf("%d",&n)==1){int i=1;while(p[i]<=n&&p[i+1]<=n){i++;}int ans=0;for(int j=1;j<i;j++){if(p[j+1]-p[j]==2)ans++;}printf("%d\n",ans);}return 0;}