素数打表（常用素数判断题节省时间复杂度）

<pre name="code" class="cpp">#include <stdio.h>#include <string.h>int a[200005];int main(){int i,j,n;memset(a,0,sizeof(a));for(i=2;i<=200000;i++){if(!a[i])for(j=i+i;j<=200000;j+=i)a[j]=1;}scanf("%d",&n);for(i=2;i<=n;i++)if(!a[i])printf("%d ",i);return 0;}