HDU 5019 Revenge of GCD

题解：筛出约数，然后计算即可。

#include <cstdio>

#include <algorithm>

typedef long long LL; 

LL a1[1000005],a2[1000005],x,y,k,g;

int cnt1,cnt2,T;

LL gcd(LL a,LL b){if(b==0)return a;else return gcd(b,a%b);}

int main(){

    scanf("%d",&T);

    while(T--){

        scanf("%I64d%I64d%I64d",&x,&y,&k);

        g=gcd(x,y); cnt1=cnt2=0;

        if(k==1){printf("%I64d\n",g);continue;}

        if(k>2000010){puts("-1");continue;}

        for(LL i=1;i*i<=g;i++)if(g%i==0){

            a1[++cnt1]=i;

            if(i*i!=g)a2[++cnt2]=g/i;

        }if(k>cnt1+cnt2)puts("-1");else if(k<=cnt2)printf("%I64d\n",a2[k]);else printf("%I64d\n",a1[cnt1-k+cnt2+1]);

    }return 0;

}

//注意循环也要用long long 否则会出错