原文链接http://www.cnblogs.com/zhouzhendong/p/8117744.html
题目传送门 - BZOJ4802
题意概括
Description
已知N，求phi(N)
Input
正整数N。N<=10^18
题解
Miller_Rabin+Pollard_Rho
至于Pollard_Rho，我感到很奇怪。判定的时候为何不能丢第一个值！！
请看下面两个代码，第一个对的，第二个错的……
代码
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <ctime>
using namespace std;
typedef long long LL;
LL gcd(LL a,LL b){
return b?gcd(b,a%b):a;
}
LL Mul(LL a,LL b,LL mod){
LL ans=0;
a%=mod;
while (b){
if (b&1)
ans=(ans+a)%mod;
b>>=1,a=(a<<1)%mod;
}
return ans;
}
LL Pow(LL a,LL b,LL mod){
LL ans=1;
a%=mod;
while (b){
if (b&1)
ans=Mul(ans,a,mod);
b>>=1,a=Mul(a,a,mod);
}
return ans;
}
bool Miller_Rabin(LL n){
if (n==2)
return 1;
if (n<2||n%2==0)
return 0;
LL m=n-1,k=0;
while (!(m&1))
m>>=1,k++;
for (int i=0;i<10;i++){
LL a=rand()%(n-1)+1,x=Pow(a,m,n),y;
for (int j=0;j<k;j++){
y=Mul(x,x,n);
if (y==1&&x!=1&&x!=n-1)
return 0;
x=y;
}
if (x!=1)
return 0;
}
return 1;
}
LL rnd(LL x,LL n,LL c){
return (Mul(x,x,n)+c)%n;
}
LL Pollard_Rho(LL n,LL c){
LL x,y;
while (1){
x=rand()%(n-1)+1,y=rnd(x,n,c);
while (1){
if (x==y)
break;
LL d=gcd(llabs(y-x)%n,n);
if (1<d&&d<n)
return d;
x=rnd(x,n,c);
y=rnd(rnd(y,n,c),n,c);
}
c=rand()%n;
}
}
LL n,x[66],pcnt;
void find(LL n){
if (n==1)
return;
if (Miller_Rabin(n)){
x[++pcnt]=n;
return;
}
LL p=Pollard_Rho(n,rand()%n);
find(p);
find(n/p);
}
int main(){
srand(19260817);
scanf("%lld",&n);
pcnt=0;
find(n);
sort(x+1,x+pcnt+1);
LL yz=pcnt?x[1]-1:1;
for (int i=2;i<=pcnt;i++)
yz=yz*(x[i]-(bool)(x[i]!=x[i-1]));
printf("%lld
",yz);
return 0;
}