bzoj1211 [HNOI2004]树的计数 prufer序列

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<vector>
#include<bitset>

using namespace std;
typedef long long LL;
int n;
int a[210];
int b[210];
void work(int x,int f)
{
for (int i=2;i<=x;i++)
{
if (x%i==0)
{
while (x%i==0) b[i]+=f,x/=i;
}
}
}
void cal(int x,int y)
{
for (int i=1;i<=x;i++)
work(i,1);
for (int i=1;i<=y;i++)
work(i,-1);
for (int i=1;i<=x-y;i++)
work(i,-1);
}
int main()
{
scanf("%d",&n);
int sum=0;
for (int i=1;i<=n;i++)
{
scanf("%d",&a[i]),sum+=a[i];
if (a[i]<=0&&n>1) return printf("0\n"),0;
}
if (sum!=2*n-2) return printf("0\n"),0;
if (n==1) return printf("1\n"),0;
sum=n-2;
for (int i=1;i<=n;i++)
cal(sum,a[i]-1),sum-=a[i]-1;
LL ans=1;
for (int i=1;i<=n;i++)
for (int j=1;j<=b[i];j++)
ans*=(LL)i;
cout<<ans<<endl;
return 0;
}