## HDU 5019 Revenge of GCD 第n个公共约数

2018年01月19日 ⁄ 综合 ⁄ 共 1403字 ⁄ 字号 评论关闭

# Revenge of GCD

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1403    Accepted Submission(s): 389

Problem Description
In mathematics, the greatest common divisor (gcd), also known as the greatest common factor (gcf), highest common factor (hcf), or greatest common measure (gcm), of two or more integers (when at least one of them is not zero), is
the largest positive integer that divides the numbers without a remainder.
---Wikipedia
Today, GCD takes revenge on you. You have to figure out the k-th GCD of X and Y.
Input
The first line contains a single integer T, indicating the number of test cases.

Each test case only contains three integers X, Y and K.
[Technical Specification]
1. 1 <= T <= 100
2. 1 <= X, Y, K <= 1 000 000 000 000
Output
For each test case, output the k-th GCD of X and Y. If no such integer exists, output -1.
Sample Input
```3
2 3 1
2 3 2
8 16 3```
Sample Output
```1
-1
2```
```/*
HDU 5019 第n个公共约数

*/
#include<iostream>
#include<stdio.h>
#include<vector>
#include<string.h>
#include<algorithm>
using namespace std;
typedef __int64 LL;
vector<LL> v;
int main()
{
LL a,b,c,r;
int t;
//	freopen("test.txt","r",stdin);
scanf("%d",&t);
while(t--)
{
scanf("%I64d%I64d%I64d",&a,&b,&c);
r=1;
while(r!=0)
{
r=b%a;
b=a;
a=r;
}
//最大公约m1
v.clear();
for(LL i=1;i*i<=b;i++)
{
if(b%i==0)
{
v.push_back(i);
if(i*i!=b)
v.push_back(b/i);
}
}
sort(v.begin(),v.end());
if(v.size()>=c)
printf("%I64d\n",v[v.size()-c]);
else
printf("-1\n");
}
return 0;
}
```