大素数测试+求最小素因子+最大素因子（模版）

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#define MAXN 10
#define C 16381
using namespace std;
typedef __int64 I64;

I64 min;

I64 multi(I64 a, I64 b, I64 n){
I64 tmp = a % n, s = 0;
while(b){
if(b & 1) s = (s + tmp) % n;
tmp = (tmp + tmp) % n;
b >>= 1;
}
return s;
}

I64 Pow(I64 a, I64 b, I64 n){
I64 tmp = a % n, s = 1;
while(b){
if(b & 1) s = multi(s, tmp, n);
tmp = multi(tmp, tmp, n);
b >>= 1;
}
return s;
}

int witness(I64 a, I64 n){
I64 u = n - 1, t = 0, i, x, y;
while(!(u & 1))    u >>= 1, t ++;
x = Pow(a, u, n);
for(i = 1; i <= t; i ++){
y = multi(x, x, n);
if(y == 1 && x != 1 && x != n -1) return 1;
x = y;
}
if(x != 1) return 1;
return 0;
}

int test(I64 n){
I64 a;
int i;
if(n == 2) return 1;
if(n < 2 || !(n & 1)) return 0;
srand((I64)time(0));
for(i = 0; i < MAXN; i ++){
a = ((I64) rand()) % (n - 2) + 2;
if(witness(a, n)) return 0;
}
return 1;
}

I64 gcd(I64 a, I64 b){
return b ? gcd(b, a % b) : a;
}

I64 pollard_rho(I64 n, I64 c){
I64 x, y, d, i = 1, k = 2;
srand((I64)time(0));
x = ((I64) rand()) % (n - 1) + 1;
y = x;
while(1){
i ++;
x = (multi(x, x, n) + c) % n;
d = gcd(y - x + n, n);
if(d != 1 && d != n) return d;
if(y == x) return n;
if(i == k) y = x, k <<= 1;
}
}

void find(I64 n, I64 c){
I64 r;
if(n <= 1) return;
if(test(n)){
if(min > n) min = n;
return;
}
r = pollard_rho(n, c--);
find(n / r, c);
find(r, c);
}

I64 MaxPrimeFactor(I64 n)
{
if(test(n))
return n;

I64 k=-1,g;
min=n;
find(n,C);

g=MaxPrimeFactor(min);
k=g>k?g:k;

g=MaxPrimeFactor(n/min);
k=g>k?g:k;
return k;
}
int main(){
I64 n;
while(~scanf("%I64d", &n))
{
// if(test(n)){                //test(n)测试n是不是素数
// printf("Prime\n");
// continue;
// }
// min = n;                   //min表示n的最小素因子
// find(n, C);                //找出n的最小素因子
// printf("%I64d\n",min);
printf("%I64d\n",MaxPrimeFactor(n));//求n的最大素因子
}
return 0;
}