LightOJ 1341 Aladdin and the Flying Carpet【整数分解】

题目链接：

题意：

分析：

代码：

#include <iostream>
#include <vector>
using namespace std;
const int maxn = 1e6 + 5;
int flag[maxn], prime[maxn];
typedef long long ll;
int tot = 0;
void getprime()
{
fill(flag, flag + maxn, 1);
for(int i = 2; i < maxn; i++){
if(flag[i]){
prime[tot++] = i;
for(int j = 2 * i; j < maxn; j += i){
flag[j] = 0;
}
}
}
}
int main (void)
{
int n;
int T;cin>>T;
getprime();
ll a, b, t;
int cas  = 1;
ll cnt;
while(T--){
cin>>a>>b;
t = a;
ll ans = 1;
if(a / b <  b)  {
cout<<"Case "<<cas<<": "<<0<<endl;
cas++;
continue;
}
for(int i = 0; i < tot && prime[i] * prime[i]<= a; i++){
cnt = 0;
while(a % prime[i] == 0){a /= prime[i]; cnt++;}
ans *= (cnt + 1);
}
if(a > 1) ans *= 2;
ans /= 2;
for(ll i = 1; i < b; i++){
if(t % i == 0)  ans--;
}
cout<<"Case "<<cas<<": "<<ans<<endl;
cas++;
}
return 0;
}