省选专练之【HNOI2004】树的计数

版权声明:LeoJAM Presents https://blog.csdn.net/fcb_x/article/details/82859960

一个有n个结点的树,设它的结点分别为v1, v2, …, vn,已知第i个结点vi的度数为di,问满足这样的条件的不同的树有多少棵。 
给定n,d1, d2, …, dn,编程需要输出满足d(vi)=di的树的个数。

第一行是一个正整数n,表示树有n个结点。第二行有n个数,第i个数表示di,即树的第i个结点的度数。其中1<=n<=150,输入数据保证满足条件的树超过10^17个。

我们知道n阶完全图的生成树个数是N^{N-2}所以先求个这个

但是由于在排列中会存在重复,固定度数的会多算,因为对于他们来说排列是没有意义的

所以除以他们的限制

但是不得house的出题人神奇的出了一个高精度

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <cassert>
#include <sstream>
#include <numeric>
#include <climits>
#include <string>
#include <cctype>
#include <ctime>
#include <iomanip>
#include <cmath>
#include <vector>
#include <queue>
#include <list>
#include <map>
#include <set>
using namespace std;
#define LL long long
#define DIGIT   4      //ËÄλ¸ô¿ª,¼´Íò½øÖÆ  
#define DEPTH   10000        //Íò½øÖÆ  
#define MAX     10000  
typedef int bignum_t[MAX+1];  
  
/************************************************************************/  
/* ¶ÁÈ¡²Ù×÷Êý£¬¶Ô²Ù×÷Êý½øÐд¦Àí´æ´¢ÔÚÊý×éÀï                             */  
/************************************************************************/  
int read(bignum_t a,istream&is=cin)  
{  
    char buf[MAX*DIGIT+1],ch ;  
    int i,j ;  
    memset((void*)a,0,sizeof(bignum_t));  
    if(!(is>>buf))return 0 ;  
    for(a[0]=strlen(buf),i=a[0]/2-1;i>=0;i--)  
    ch=buf[i],buf[i]=buf[a[0]-1-i],buf[a[0]-1-i]=ch ;  
    for(a[0]=(a[0]+DIGIT-1)/DIGIT,j=strlen(buf);j<a[0]*DIGIT;buf[j++]='0');  
    for(i=1;i<=a[0];i++)  
    for(a[i]=0,j=0;j<DIGIT;j++)  
    a[i]=a[i]*10+buf[i*DIGIT-1-j]-'0' ;  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
    return 1 ;  
}  
  
void write(const bignum_t a,ostream&os=cout)  
{  
    int i,j ;  
    for(os<<a[i=a[0]],i--;i;i--)  
    for(j=DEPTH/10;j;j/=10)  
    os<<a[i]/j%10 ;  
}  
  
int comp(const bignum_t a,const bignum_t b)  
{  
    int i ;  
    if(a[0]!=b[0])  
    return a[0]-b[0];  
    for(i=a[0];i;i--)  
    if(a[i]!=b[i])  
    return a[i]-b[i];  
    return 0 ;  
}  
  
int comp(const bignum_t a,const int b)  
{  
    int c[12]={1};  
    for(c[1]=b;c[c[0]]>=DEPTH;c[c[0]+1]=c[c[0]]/DEPTH,c[c[0]]%=DEPTH,c[0]++);  
    return comp(a,c);  
}  
  
int comp(const bignum_t a,const int c,const int d,const bignum_t b)  
{  
    int i,t=0,O=-DEPTH*2 ;  
    if(b[0]-a[0]<d&&c)  
    return 1 ;  
    for(i=b[0];i>d;i--)  
    {  
        t=t*DEPTH+a[i-d]*c-b[i];  
        if(t>0)return 1 ;  
        if(t<O)return 0 ;  
    }  
    for(i=d;i;i--)  
    {  
        t=t*DEPTH-b[i];  
        if(t>0)return 1 ;  
        if(t<O)return 0 ;  
    }  
    return t>0 ;  
}  
/************************************************************************/  
/* ´óÊýÓë´óÊýÏà¼Ó                                                       */  
/************************************************************************/  

void add(bignum_t a,const bignum_t b)  
{  
    int i ;  
    for(i=1;i<=b[0];i++)  
    if((a[i]+=b[i])>=DEPTH)  
    a[i]-=DEPTH,a[i+1]++;  
    if(b[0]>=a[0])  
    a[0]=b[0];  
    else  
    for(;a[i]>=DEPTH&&i<a[0];a[i]-=DEPTH,i++,a[i]++);  
    a[0]+=(a[a[0]+1]>0);  
}  
/************************************************************************/  
/* ´óÊýÓëСÊýÏà¼Ó                                                       */  
/************************************************************************/  

void add(bignum_t a,const int b)  
{  
    int i=1 ;  
    for(a[1]+=b;a[i]>=DEPTH&&i<a[0];a[i+1]+=a[i]/DEPTH,a[i]%=DEPTH,i++);  
    for(;a[a[0]]>=DEPTH;a[a[0]+1]=a[a[0]]/DEPTH,a[a[0]]%=DEPTH,a[0]++);  
}  

/************************************************************************/  
/* ´óÊýÏà¼õ(±»¼õÊý>=¼õÊý)                                               */  
/************************************************************************/  

void sub(bignum_t a,const bignum_t b)  
{  
    int i ;  
    for(i=1;i<=b[0];i++)  
    if((a[i]-=b[i])<0)  
    a[i+1]--,a[i]+=DEPTH ;  
    for(;a[i]<0;a[i]+=DEPTH,i++,a[i]--);  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
}  

/************************************************************************/  
/* ´óÊý¼õȥСÊý(±»¼õÊý>=¼õÊý)                                           */  
/************************************************************************/  

void sub(bignum_t a,const int b)  
{  
    int i=1 ;  
    for(a[1]-=b;a[i]<0;a[i+1]+=(a[i]-DEPTH+1)/DEPTH,a[i]-=(a[i]-DEPTH+1)/DEPTH*DEPTH,i++);  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
}  
  
void sub(bignum_t a,const bignum_t b,const int c,const int d)  
{  
    int i,O=b[0]+d ;  
    for(i=1+d;i<=O;i++)  
    if((a[i]-=b[i-d]*c)<0)  
    a[i+1]+=(a[i]-DEPTH+1)/DEPTH,a[i]-=(a[i]-DEPTH+1)/DEPTH*DEPTH ;  
    for(;a[i]<0;a[i+1]+=(a[i]-DEPTH+1)/DEPTH,a[i]-=(a[i]-DEPTH+1)/DEPTH*DEPTH,i++);  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
}  

/************************************************************************/  
/* ´óÊýÏà³Ë£¬¶ÁÈë±»³ËÊýa£¬³ËÊýb£¬½á¹û±£´æÔÚc[]                          */  
/************************************************************************/  

void mul(bignum_t c,const bignum_t a,const bignum_t b)  
{  
    int i,j ;  
    memset((void*)c,0,sizeof(bignum_t));  
    for(c[0]=a[0]+b[0]-1,i=1;i<=a[0];i++)  
    for(j=1;j<=b[0];j++)  
    if((c[i+j-1]+=a[i]*b[j])>=DEPTH)  
    c[i+j]+=c[i+j-1]/DEPTH,c[i+j-1]%=DEPTH ;  
    for(c[0]+=(c[c[0]+1]>0);!c[c[0]]&&c[0]>1;c[0]--);  
}  

/************************************************************************/  
/* ´óÊý³ËÒÔСÊý£¬¶ÁÈë±»³ËÊýa£¬³ËÊýb£¬½á¹û±£´æÔÚ±»³ËÊý                   */  
/************************************************************************/  

void mul(bignum_t a,const int b)  
{  
    int i ;  
    for(a[1]*=b,i=2;i<=a[0];i++)  
    {  
        a[i]*=b ;  
        if(a[i-1]>=DEPTH)  
        a[i]+=a[i-1]/DEPTH,a[i-1]%=DEPTH ;  
    }  
    for(;a[a[0]]>=DEPTH;a[a[0]+1]=a[a[0]]/DEPTH,a[a[0]]%=DEPTH,a[0]++);  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
}  
  
void mul(bignum_t b,const bignum_t a,const int c,const int d)  
{  
    int i ;  
    memset((void*)b,0,sizeof(bignum_t));  
    for(b[0]=a[0]+d,i=d+1;i<=b[0];i++)  
    if((b[i]+=a[i-d]*c)>=DEPTH)  
    b[i+1]+=b[i]/DEPTH,b[i]%=DEPTH ;  
    for(;b[b[0]+1];b[0]++,b[b[0]+1]=b[b[0]]/DEPTH,b[b[0]]%=DEPTH);  
    for(;!b[b[0]]&&b[0]>1;b[0]--);  
}  

/**************************************************************************/  
/* ´óÊýÏà³ý,¶ÁÈë±»³ýÊýa£¬³ýÊýb£¬½á¹û±£´æÔÚc[]Êý×é                         */  
/* ÐèÒªcomp()º¯Êý                                                         */  
/**************************************************************************/  

void div(bignum_t c,bignum_t a,const bignum_t b)  
{  
    int h,l,m,i ;  
    memset((void*)c,0,sizeof(bignum_t));  
    c[0]=(b[0]<a[0]+1)?(a[0]-b[0]+2):1 ;  
    for(i=c[0];i;sub(a,b,c[i]=m,i-1),i--)  
    for(h=DEPTH-1,l=0,m=(h+l+1)>>1;h>l;m=(h+l+1)>>1)  
    if(comp(b,m,i-1,a))h=m-1 ;  
    else l=m ;  
    for(;!c[c[0]]&&c[0]>1;c[0]--);  
    c[0]=c[0]>1?c[0]:1 ;  
}  
  
void div(bignum_t a,const int b,int&c)  
{  
    int i ;  
    for(c=0,i=a[0];i;c=c*DEPTH+a[i],a[i]=c/b,c%=b,i--);  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
}  

/************************************************************************/  
/* ´óÊýƽ·½¸ù£¬¶ÁÈë´óÊýa£¬½á¹û±£´æÔÚb[]Êý×éÀï                           */  
/* ÐèÒªcomp()º¯Êý                                                       */  
/************************************************************************/  

void sqrt(bignum_t b,bignum_t a)  
{  
    int h,l,m,i ;  
    memset((void*)b,0,sizeof(bignum_t));  
    for(i=b[0]=(a[0]+1)>>1;i;sub(a,b,m,i-1),b[i]+=m,i--)  
    for(h=DEPTH-1,l=0,b[i]=m=(h+l+1)>>1;h>l;b[i]=m=(h+l+1)>>1)  
    if(comp(b,m,i-1,a))h=m-1 ;  
    else l=m ;  
    for(;!b[b[0]]&&b[0]>1;b[0]--);  
    for(i=1;i<=b[0];b[i++]>>=1);  
}  

/************************************************************************/  
/* ·µ»Ø´óÊýµÄ³¤¶È                                                       */  
/************************************************************************/  

int length(const bignum_t a)  
{  
    int t,ret ;  
    for(ret=(a[0]-1)*DIGIT,t=a[a[0]];t;t/=10,ret++);  
    return ret>0?ret:1 ;  
}  

/************************************************************************/  
/* ·µ»ØÖ¸¶¨Î»ÖõÄÊý×Ö£¬´ÓµÍλ¿ªÊ¼Êýµ½µÚb룬·µ»ØbλÉϵÄÊý               */  
/************************************************************************/  

int digit(const bignum_t a,const int b)  
{  
    int i,ret ;  
    for(ret=a[(b-1)/DIGIT+1],i=(b-1)%DIGIT;i;ret/=10,i--);  
    return ret%10 ;  
}  

/************************************************************************/  
/* ·µ»Ø´óÊýĩβ0µÄ¸öÊý                                                  */  
/************************************************************************/  

int zeronum(const bignum_t a)  
{  
    int ret,t ;  
    for(ret=0;!a[ret+1];ret++);  
    for(t=a[ret+1],ret*=DIGIT;!(t%10);t/=10,ret++);  
    return ret ;  
}  
  
void comp(int*a,const int l,const int h,const int d)  
{  
    int i,j,t ;  
    for(i=l;i<=h;i++)  
    for(t=i,j=2;t>1;j++)  
    while(!(t%j))  
    a[j]+=d,t/=j ;  
}  
  
void convert(int*a,const int h,bignum_t b)  
{  
    int i,j,t=1 ;  
    memset(b,0,sizeof(bignum_t));  
    for(b[0]=b[1]=1,i=2;i<=h;i++)  
    if(a[i])  
    for(j=a[i];j;t*=i,j--)  
    if(t*i>DEPTH)  
    mul(b,t),t=1 ;  
    mul(b,t);  
}  
  
#define SGN(x) ((x)>0?1:((x)<0?-1:0))  
#define ABS(x) ((x)>0?(x):-(x))  
  
int read(bignum_t a,int&sgn,istream&is=cin)  
{  
    char str[MAX*DIGIT+2],ch,*buf ;  
    int i,j ;  
    memset((void*)a,0,sizeof(bignum_t));  
    if(!(is>>str))return 0 ;  
    buf=str,sgn=1 ;  
    if(*buf=='-')sgn=-1,buf++;  
    for(a[0]=strlen(buf),i=a[0]/2-1;i>=0;i--)  
    ch=buf[i],buf[i]=buf[a[0]-1-i],buf[a[0]-1-i]=ch ;  
    for(a[0]=(a[0]+DIGIT-1)/DIGIT,j=strlen(buf);j<a[0]*DIGIT;buf[j++]='0');  
    for(i=1;i<=a[0];i++)  
    for(a[i]=0,j=0;j<DIGIT;j++)  
    a[i]=a[i]*10+buf[i*DIGIT-1-j]-'0' ;  
    for(;!a[a[0]]&&a[0]>1;a[0]--);  
    if(a[0]==1&&!a[1])sgn=0 ;  
    return 1 ;  
}  
struct bignum  
{  
    bignum_t num ;  
    int sgn ;  
    public :  
    inline bignum()  
    {  
        memset(num,0,sizeof(bignum_t));  
        num[0]=1 ;  
        sgn=0 ;  
    }  
    inline int operator!()  
    {  
        return num[0]==1&&!num[1];  
    }  
    inline bignum&operator=(const bignum&a)  
    {  
        memcpy(num,a.num,sizeof(bignum_t));  
        sgn=a.sgn ;  
        return*this ;  
    }  
    inline bignum&operator=(const int a)  
    {  
        memset(num,0,sizeof(bignum_t));  
        num[0]=1 ;  
        sgn=SGN (a);  
        add(num,sgn*a);  
        return*this ;  
    }  
    ;  
    inline bignum&operator+=(const bignum&a)  
    {  
        if(sgn==a.sgn)add(num,a.num);  
        else if  
        (sgn&&a.sgn)  
        {  
            int ret=comp(num,a.num);  
            if(ret>0)sub(num,a.num);  
            else if(ret<0)  
            {  
                bignum_t t ;  
                memcpy(t,num,sizeof(bignum_t));  
                memcpy(num,a.num,sizeof(bignum_t));  
                sub (num,t);  
                sgn=a.sgn ;  
            }  
            else memset(num,0,sizeof(bignum_t)),num[0]=1,sgn=0 ;  
        }  
        else if(!sgn)  
            memcpy(num,a.num,sizeof(bignum_t)),sgn=a.sgn ;  
        return*this ;  
    }  
    inline bignum&operator+=(const int a)  
    {  
        if(sgn*a>0)add(num,ABS(a));  
        else if(sgn&&a)  
        {  
            int  ret=comp(num,ABS(a));  
            if(ret>0)sub(num,ABS(a));  
            else if(ret<0)  
            {  
                bignum_t t ;  
                memcpy(t,num,sizeof(bignum_t));  
                memset(num,0,sizeof(bignum_t));  
                num[0]=1 ;  
                add(num,ABS (a));  
                sgn=-sgn ;  
                sub(num,t);  
            }  
            else memset(num,0,sizeof(bignum_t)),num[0]=1,sgn=0 ;  
        }  
        else if  
            (!sgn)sgn=SGN(a),add(num,ABS(a));  
        return*this ;  
    }  
    inline bignum operator+(const bignum&a)  
    {  
        bignum ret ;  
        memcpy(ret.num,num,sizeof (bignum_t));  
        ret.sgn=sgn ;  
        ret+=a ;  
        return ret ;  
    }  
    inline bignum operator+(const int a)  
    {  
        bignum ret ;  
        memcpy(ret.num,num,sizeof (bignum_t));  
        ret.sgn=sgn ;  
        ret+=a ;  
        return ret ;  
    }  
    inline bignum&operator-=(const bignum&a)  
    {  
        if(sgn*a.sgn<0)add(num,a.num);  
        else if  
        (sgn&&a.sgn)  
        {  
            int ret=comp(num,a.num);  
            if(ret>0)sub(num,a.num);  
            else if(ret<0)  
            {  
                bignum_t t ;  
                memcpy(t,num,sizeof(bignum_t));  
                memcpy(num,a.num,sizeof(bignum_t));  
                sub(num,t);  
                sgn=-sgn ;  
            }  
            else memset(num,0,sizeof(bignum_t)),num[0]=1,sgn=0 ;  
        }  
        else if(!sgn)add (num,a.num),sgn=-a.sgn ;  
        return*this ;  
    }  
    inline bignum&operator-=(const int a)  
    {  
        if(sgn*a<0)add(num,ABS(a));  
        else if(sgn&&a)  
        {  
            int  ret=comp(num,ABS(a));  
            if(ret>0)sub(num,ABS(a));  
            else if(ret<0)  
            {  
                bignum_t t ;  
                memcpy(t,num,sizeof(bignum_t));  
                memset(num,0,sizeof(bignum_t));  
                num[0]=1 ;  
                add(num,ABS(a));  
                sub(num,t);  
                sgn=-sgn ;  
            }  
            else memset(num,0,sizeof(bignum_t)),num[0]=1,sgn=0 ;  
        }  
        else if  
            (!sgn)sgn=-SGN(a),add(num,ABS(a));  
        return*this ;  
    }  
    inline bignum operator-(const bignum&a)  
    {  
        bignum ret ;  
        memcpy(ret.num,num,sizeof(bignum_t));  
        ret.sgn=sgn ;  
        ret-=a ;  
        return ret ;  
    }  
    inline bignum operator-(const int a)  
    {  
        bignum ret ;  
        memcpy(ret.num,num,sizeof(bignum_t));  
        ret.sgn=sgn ;  
        ret-=a ;  
        return ret ;  
    }  
    inline bignum&operator*=(const bignum&a)  
    {  
        bignum_t t ;  
        mul(t,num,a.num);  
        memcpy(num,t,sizeof(bignum_t));  
        sgn*=a.sgn ;  
        return*this ;  
    }  
    inline bignum&operator*=(const int a)  
    {  
        mul(num,ABS(a));  
        sgn*=SGN(a);  
        return*this ;  
    }  
    inline bignum operator*(const bignum&a)  
    {  
        bignum ret ;  
        mul(ret.num,num,a.num);  
        ret.sgn=sgn*a.sgn ;  
        return ret ;  
    }  
    inline bignum operator*(const int a)  
    {  
        bignum ret ;  
        memcpy(ret.num,num,sizeof (bignum_t));  
        mul(ret.num,ABS(a));  
        ret.sgn=sgn*SGN(a);  
        return ret ;  
    }  
    inline bignum&operator/=(const bignum&a)  
    {  
        bignum_t t ;  
        div(t,num,a.num);  
        memcpy (num,t,sizeof(bignum_t));  
        sgn=(num[0]==1&&!num[1])?0:sgn*a.sgn ;  
        return*this ;  
    }  
    inline bignum&operator/=(const int a)  
    {  
        int t ;  
        div(num,ABS(a),t);  
        sgn=(num[0]==1&&!num [1])?0:sgn*SGN(a);  
        return*this ;  
    }  
    inline bignum operator/(const bignum&a)  
    {  
        bignum ret ;  
        bignum_t t ;  
        memcpy(t,num,sizeof(bignum_t));  
        div(ret.num,t,a.num);  
        ret.sgn=(ret.num[0]==1&&!ret.num[1])?0:sgn*a.sgn ;  
        return ret ;  
    }  
    inline bignum operator/(const int a)  
    {  
        bignum ret ;  
        int t ;  
        memcpy(ret.num,num,sizeof(bignum_t));  
        div(ret.num,ABS(a),t);  
        ret.sgn=(ret.num[0]==1&&!ret.num[1])?0:sgn*SGN(a);  
        return ret ;  
    }  
    inline bignum&operator%=(const bignum&a)  
    {  
        bignum_t t ;  
        div(t,num,a.num);  
        if(num[0]==1&&!num[1])sgn=0 ;  
        return*this ;  
    }  
    inline int operator%=(const int a)  
    {  
        int t ;  
        div(num,ABS(a),t);  
        memset(num,0,sizeof (bignum_t));  
        num[0]=1 ;  
        add(num,t);  
        return t ;  
    }  
    inline bignum operator%(const bignum&a)  
    {  
        bignum ret ;  
        bignum_t t ;  
        memcpy(ret.num,num,sizeof(bignum_t));  
        div(t,ret.num,a.num);  
        ret.sgn=(ret.num[0]==1&&!ret.num [1])?0:sgn ;  
        return ret ;  
    }  
    inline int operator%(const int a)  
    {  
        bignum ret ;  
        int t ;  
        memcpy(ret.num,num,sizeof(bignum_t));  
        div(ret.num,ABS(a),t);  
        memset(ret.num,0,sizeof(bignum_t));  
        ret.num[0]=1 ;  
        add(ret.num,t);  
        return t ;  
    }  
    inline bignum&operator++()  
    {  
        *this+=1 ;  
        return*this ;  
    }  
    inline bignum&operator--()  
    {  
        *this-=1 ;  
        return*this ;  
    }  
    ;  
    
    inline int operator>(const bignum&a)  
    {  
        return sgn>0?(a.sgn>0?comp(num,a.num)>0:1):(sgn<0?(a.sgn<0?comp(num,a.num)<0:0):a.sgn<0);  
    }  
    ;
    
    inline int operator>(const int a)  
    {  
        return sgn>0?(a>0?comp(num,a)>0:1):(sgn<0?(a<0?comp(num,-a)<0:0):a<0);  
    }  
    ;
    
    inline int operator>=(const bignum&a)  
    {  
        return sgn>0?(a.sgn>0?comp(num,a.num)>=0:1):(sgn<0?(a.sgn<0?comp(num,a.num)<=0:0):a.sgn<=0);  
    }  
    ;
    
    inline int operator>=(const int a)  
    {  
        return sgn>0?(a>0?comp(num,a)>=0:1):(sgn<0?(a<0?comp(num,-a)<=0:0):a<=0);  
    }  
    ;
    
    inline int operator<(const bignum&a)  
    {  
        return sgn<0?(a.sgn<0?comp(num,a.num)>0:1):(sgn>0?(a.sgn>0?comp(num,a.num)<0:0):a.sgn>0);  
    }  
    ;
    
    inline int operator<(const int a)  
    {  
        return sgn<0?(a<0?comp(num,-a)>0:1):(sgn>0?(a>0?comp(num,a)<0:0):a>0);  
    }  
    ;
    
    inline int operator<=(const bignum&a)  
    {  
        return sgn<0?(a.sgn<0?comp(num,a.num)>=0:1):(sgn>0?(a.sgn>0?comp(num,a.num)<=0:0):a.sgn>=0);  
    }  
    ;
    
    inline int operator<=(const int a)  
    {  
        return sgn<0?(a<0?comp(num,-a)>=0:1):  
        (sgn>0?(a>0?comp(num,a)<=0:0):a>=0);  
    }  
    ;
    
    inline int operator==(const bignum&a)  
    {  
        return(sgn==a.sgn)?!comp(num,a.num):0 ;  
    }  
    ;
    
    inline int operator==(const int a)  
    {  
        return(sgn*a>=0)?!comp(num,ABS(a)):0 ;  
    }  
    ;
    
    inline int operator!=(const bignum&a)  
    {  
        return(sgn==a.sgn)?comp(num,a.num):1 ;  
    }  
    ;
    
    inline int operator!=(const int a)  
    {  
        return(sgn*a>=0)?comp(num,ABS(a)):1 ;  
    }  
    ;
    
    inline int operator[](const int a)  
    {  
        return digit(num,a);  
    }  
    ;
    
    friend inline istream&operator>>(istream&is,bignum&a)  
    {  
        read(a.num,a.sgn,is);  
        return  is ;  
    }  
    ;
    
    friend inline ostream&operator<<(ostream&os,const bignum&a)  
    {  
        if(a.sgn<0)  
            os<<'-' ;  
        write(a.num,os);  
        return os ;  
    }  
    ;
    
    friend inline bignum sqrt(const bignum&a)  
    {  
        bignum ret ;  
        bignum_t t ;  
        memcpy(t,a.num,sizeof(bignum_t));  
        sqrt(ret.num,t);  
        ret.sgn=ret.num[0]!=1||ret.num[1];  
        return ret ;  
    }  
    ;
    
    friend inline bignum sqrt(const bignum&a,bignum&b)  
    {  
        bignum ret ;  
        memcpy(b.num,a.num,sizeof(bignum_t));  
        sqrt(ret.num,b.num);  
        ret.sgn=ret.num[0]!=1||ret.num[1];  
        b.sgn=b.num[0]!=1||ret.num[1];  
        return ret ;  
    }  
    ;
    
    inline int length()  
    {  
        return :: length(num);  
    }  
    ;
    
    inline int zeronum()  
    {  
        return :: zeronum(num);  
    }   
    ;
    
}ans;

bignum C(bignum n,bignum m)
{
    ans=1;bignum maxx=n-m;
    for(int i=1;maxx>=i;++i)ans=ans*(m+i)/i;
    return ans;
}

const int MOD=3389;

LL ksm(LL a,LL b)
{
    LL ans=1;
    for(;b;b>>=1,a=a*a%MOD)if(b&1)ans=ans*a%MOD;
    return ans;
}
const int N=200;
int vis[N];
int Prime[N];
int cnt=0;
void Pre(){
	for(int i=2;i<N;++i){
		if(!vis[i]){
			Prime[++cnt]=i;
		}
		for(int j=1;j<=cnt&&i*Prime[j]<N;++j){
			vis[i*Prime[j]]++;
			if(i%Prime[j]==0)break;
		}
	}
}
int A[N];
int B[N];
int D[N];
void Solve(int *X,int sum){
//	cout<<sum<<'\n';
	memset(X,0,sizeof(X));
	if(!sum)return;
	for(int i=1;i<=cnt;++i){
		int now=Prime[i];
		while(1){
			X[i]+=sum/now;
			now=now*Prime[i];
			if(now>sum)break;
		}
	}
}
int n;
int Quick_Pow(int x,int k){
	cout<<x<<" "<<k<<'\n';
	int ret=1;
	while(k){
		if(k%2){
			ret=ret*x;
		}
		k/=2;
		x=x*x;
	}
	cout<<ret<<'\n';
	return ret;
}
int main(){
//	freopen("test.in","r",stdin);
	Pre();
	cin>>n;
	int tot=0;
	for(int i=1;i<=n;++i){
		cin>>D[i];
		tot+=D[i];
		if(!D[i]&&n>1){
			cout<<0;
			return 0;
		}
	}
	if(tot!=2*n-2){
		cout<<0;
		return 0;
	}
	if(n<=1){
		cout<<1;
		return 0;
	}
	Solve(A,n-2);
	for(int i=1;i<=n;++i){
		memset(B,0,sizeof(B));
		Solve(B,D[i]-1);
		for(int j=1;j<=cnt;++j){
			A[j]-=B[j];
		}
	}
	ans=1;
	for(int i=1;i<=cnt;++i){
//		cout<<A[i]<<" "<<Prime[i]<<'\n';
		if(A[i]){
			for(int j=1;j<=A[i];++j)
				ans=ans*Prime[i];
		}
	}
	cout<<ans;
}

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转载自blog.csdn.net/fcb_x/article/details/82859960