BZOJ1211: [HNOI2004]树的计数

题目：http://www.lydsy.com/JudgeOnline/problem.php?id=1211

依然是prufer编码，然后注意一下坑点。

#include<cstring>
#include<cstdio>
#include<algorithm>
#include<iostream>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define down(i,l,r) for (int i=l;i>=r;i--)
#define clr(x,y) memset(x,y,sizeof(x))
#define maxn 100500
#define ll long long
using namespace std;
ll ans,d[maxn];
int pri[maxn],num[maxn],vis[maxn],tot,sum;
int n;
ll read(){
    ll x=0,f=1; char ch=getchar();
    while (!isdigit(ch)) {if (ch=='-') f=-1; ch=getchar();}
    while (isdigit(ch)) {x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}
void pre(){
    rep(i,2,200){
        if (!vis[i]) vis[i]=1,pri[++tot]=i;
        rep(j,1,tot) {
            if (i*pri[j]>200) break;
            vis[i*pri[j]]=1;
            if (i%pri[j]==0) break;
        }
    }
}
void get(int x,int v){
    int now=1;
    while (x!=1){
        while (x%pri[now]==0) x/=pri[now],num[now]+=v;
        now++;
    }
}
int main(){
      pre();
    scanf("%d",&n);
      int len=n-2; int gg=0;
      rep(i,1,n){
          d[i]=read();
          if (d[i]==0) {gg=1; break;}
          sum+=d[i]-1;
      }
      if (n==1&&!d[1]) {puts("1"); return 0;}
    if (sum!=len) gg=1;
      if (gg) {puts("0"); return 0;}
    ans=1;
      rep(i,1,sum) get(i,1);
      rep(i,1,n) {
          rep(j,1,d[i]-1) get(j,-1);
      }
      rep(i,1,tot) if (num[i]) {
          rep(j,1,num[i]) ans=ans*(ll)pri[i];
      } 
      printf("%lld
",ans);
    return 0;
}