poj 2262

很基础的一道数学题，不过感觉跑的太慢啊，422ms

#include <iostream>#include <cmath>using namespace std;const int maxn=1000001;int vis[maxn],p[maxn];int t;void prime(){t=0;int i,j;int n=(int)sqrt(maxn-1);for(i=2;i<=n;i++){if(!vis[i]){p[t++]=i;for(j=i*i;j<=maxn-1;j+=i)vis[j]=1;}}}int main(){int n;prime();while(cin>>n&&n!=0){int a,b;int i,j=0;bool flag1=true,flag2=true;for(i=p[j];i<=(n/2);i=p[++j]){if(!vis[n-i]){flag1=flag2=false;cout<<n<<" = "<<i<<" + "<<n-i<<endl;break;}}if(flag1){j=t-1;for(i=p[j];;i=p[--j]){if(!vis[n-i]){cout<<n<<" = "<<i<<" + "<<n-i<<endl;flag2=false;break;}}}if(flag2)cout<<"Goldbach's conjecture is wrong." <<endl;}return 0;}