[poj] 3421 X-factor Chains

原题

就是n的所有质因子的全排列（是可重集全排列）

#include<cstdio>
#include<cstring>
#define N 2020
typedef long long ll;
using namespace std;
ll jc[22],cnt,n,prime[N],ans,sum;
int num[N];
bool is[N];

int main()
{
    jc[0]=1;
    for (int i=1;i<=20;i++) jc[i]=jc[i-1]*i;
    for (int i=2;i<=2000;i++) is[i]=1;
    for (int i=2;i<=2000;i++)
	if (is[i])
	{
	    prime[++cnt]=i;
	    for (int j=i*i;j<=2000;j+=i)
		is[j]=0;
	} 
    while (~scanf("%lld",&n))
    {
	ans=0;
	sum=0;
	memset(num,0,sizeof(num));
	for (int i=1;i<=cnt;i++)
	{
	    if (n==1) break;
	    while (n%prime[i]==0) n/=prime[i],num[i]++,sum++;
	}
	if (n>1) sum++;
	ans=jc[sum];
	for (int i=1;i<=cnt;i++)
	    ans/=jc[num[i]];
	printf("%lld %lld\n",sum,ans);
    }
    return 0;
}