P2290 [HNOI2004]树的计数

P2290 [HNOI2004]树的计数
prufer序列模板题

#include <iostream>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#define inf 2147483647
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(long long i=a;i<=b;++i)
//by war
//2019.8.26
using namespace std;
long long n,sum,flag,cnt,temp,ans;
long long a[N],prime[N],tot[N];
bool vis[N];
void in(long long &x){
    long long y=;char c=getchar();x=;
    while(c<''||c>''){if(c=='-')y=-;c=getchar();}
    while(c<=''&&c>=''){ x=(x<<)+(x<<)+c-'';c=getchar();}
    x*=y;
}
void o(long long x){
    if(x<){p('-');x=-x;}
    if(x>)o(x/);
    p(x%+'');
}

void Euler(){
    for(long long i=;i<=;i++){
        if(!vis[i]) prime[++cnt]=i;
        for(long long j=;j<=cnt&&i*prime[j]<=;j++){
            vis[i*prime[j]]=;
            if(i%prime[j]==)
            break;
        }
    }
}

long long ksm(long long a,long long b){
    long long r=;
    while(b>){
        if(b&) r*=a;
        a*=a;
        b>>=;
    }
    return r;
}

signed main(){
    in(n);Euler();
    For(i,,n){
        in(a[i]),sum+=a[i]-;
        if(!a[i]) flag=;
    }
    if(n==&&flag){
        o(); return ;
    }
    if(sum!=n-||flag){
        o(); return ;
    }
    For(i,,n-){
        temp=i;
        For(j,,cnt)
            while(temp%prime[j]==){
                tot[prime[j]]++;
                temp/=prime[j];
            }
    }
    For(i,,n)
        For(j,,a[i]-){
            temp=j;
            For(k,,cnt)
                while(temp%prime[k]==){
                    tot[prime[k]]--;
                    temp/=prime[k];
                }
        }
    ans=;
    For(i,,cnt)
        ans*=ksm(prime[i],tot[prime[i]]);
    o(ans);
    return ;
}