hdu 5108——Alexandra and Prime Numbers

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;

const int maxn=1000005;
bool valid[maxn];
int prime[maxn];
void getprime(int n,int &tot,int ans[maxn])
{
        memset(valid,1,sizeof(valid));
        for(int i=2;i<=n;++i){
                if(valid[i]){
                        tot++;
                        ans[tot]=i;
                }
                for(int j=1;((j<=tot)&&(i*ans[j]<=n));j++){
                        valid[i*ans[j]]=false;
                        if(i%ans[j]==0)break;
                }
        }
}

int factot(int n,int tot)
{
        int tmp,i,now;
        tmp=(int)((double)sqrt(n)+1);
        now=n;
        int ret=0;
        for(i=1;i<=tot;++i){
                if(now%prime[i]==0){
                        while(now%prime[i]==0){
                                ret=max(ret,prime[i]);
                                now/=prime[i];
                        }
                }
        }
        if(now!=1)ret=max(ret,now);
        return ret;
}

int main()
{
//        freopen("data.txt","r",stdin);
        int tot=0;
        getprime(maxn,tot,prime);
        int n;
        while(scanf("%d",&n)!=EOF)
        {
                int ans=factot(n,tot);
                printf("%d\n",ans?n/ans:0);
        }
        return 0;
}