hdu 5428 The Factor(素数筛选合数分解)

#include<cstdio>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
int t,n,m;
int num[505];
const int MAXN=100000;
int prime[MAXN+1];
void getprime(){
  memset(prime,0,sizeof(prime));
  for(int i=2;i<=MAXN;i++){
    if(!prime[i]) prime[++prime[0]]=i;
    for(int j=1;j<=prime[0]&&prime[j]*i<=MAXN;j++){
        prime[prime[j]*i]=1;
        if(i%prime[j]==0) break;
    }
  }
}
long long factor[100][2];
int cnt;
int getfactor(long long x){
  cnt=0;
  long long tmp=x;
  for(int i=1;prime[i]<=tmp/prime[i];i++){
    factor[cnt][1]=0;
    if(tmp%prime[i]==0){
        factor[cnt][0]=prime[i];
        while(tmp%prime[i]==0){
            factor[cnt][1]++;
            tmp/=prime[i];
        }
        cnt++;
    }
  }
  if(tmp!=1){
    factor[cnt][0]=tmp;
    factor[cnt++][1]=1;
  }
  return cnt;
}
int main(){
    int i,j,k;
    getprime();
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        vector<int> ans;
        for(i=0;i<n;i++){
            scanf("%d",&num[i]);
            getfactor(num[i]);
            for(j=0;j<cnt;j++){
                while(factor[j][1]--){
                    ans.push_back(factor[j][0]);
                }
            }
        }
        sort(ans.begin(),ans.end());
        if(ans.size()<2){
            printf("-1\n");
        }
        else{
            printf("%I64d\n",(long long)ans[0]*ans[1]);
        }
    }
    return 0;
}