#include <bits/stdc++.h>
using namespace std;
map<int,int>ma;
const long long MOD=1000000007;
bool elim[432000010];
inline long long putere(long long a,long long b)
{
if(b==0)
return 1;
long long p=putere(a,b/2);
p*=p;
p%=MOD;
if(b%2)
{
p*=a;
p%=MOD;
}
return p;
}
long long fact[610],comb[610][610];
inline void factorial()
{
fact[0]=1;
for(long long i=1;i<=600;++i)
fact[i]=fact[i-1]*i%MOD;
}
inline long long combinari(long long n,long long m)
{
long long ans=1;
ans=fact[n];
ans*=putere(fact[m],MOD-2);
ans%=MOD;
ans*=putere(fact[n-m],MOD-2);
ans%=MOD;
return ans;
}
long long n,v[610];
inline long long cod(long long step,long long nrstack,long long ppoz,bool exista)
{
return (((step-1)*600+nrstack-1)*600+ppoz-1)*2+exista-1;
}
inline long long raspunde(long long step,long long nrstack,long long ppoz,bool exista)
{
if(elim[cod(step,nrstack,ppoz,exista)])
return ma[cod(step,nrstack,ppoz,exista)];
if(step==n)
{
elim[cod(step,nrstack,ppoz,exista)]=true;
ma[cod(step,nrstack,ppoz,exista)]=1;
return 1;
}
long long ans=0;
long long ramas=n-step-nrstack;
long long posibileInceput=v[ppoz]-1-(2*step-step+ppoz-1-nrstack);
if(exista==false)
{
if(ramas>=3)
ans=(ans+comb[ramas-1][2]*raspunde(step+1,nrstack+1,ppoz,false))%MOD;
if(ramas>=2)
ans=(ans+(ramas-1)*raspunde(step+1,nrstack+1,ppoz,true))%MOD;
if(posibileInceput>=2&&nrstack>=1)
ans=(ans+comb[posibileInceput][2]*raspunde(step+1,nrstack-1,ppoz,false))%MOD;
if(posibileInceput&&nrstack>=1&&ramas>=1)
{
if(ramas-1)
ans=(ans+posibileInceput*(ramas-1)%MOD*raspunde(step+1,nrstack,ppoz,false))%MOD;
ans=(ans+posibileInceput*raspunde(step+1,nrstack,ppoz,true))%MOD;
}
else if(posibileInceput&&ramas>=1)
{
if(step==n-1)
{
elim[cod(step,nrstack,ppoz,exista)]=true;
ma[cod(step,nrstack,ppoz,exista)]=1;
return 1;
}
if(ramas-1)
ans=(ans+posibileInceput*(ramas-1)%MOD*raspunde(step+1,nrstack,ppoz,false))%MOD;
long long q=putere(comb[n-ppoz][step+1-ppoz],MOD-2);
for(int newppoz=ppoz+1;newppoz<=step+2;++newppoz)
ans=(ans+comb[n-newppoz][step+2-newppoz]*q%MOD*posibileInceput%MOD*raspunde(step+1,nrstack,newppoz,false))%MOD;
}
}
else
{
if(ramas>=2)
ans=(ans+comb[ramas][2]*raspunde(step+1,nrstack+1,ppoz,true))%MOD;
if(posibileInceput>=2)
{
if(nrstack>=2)
ans=(ans+comb[posibileInceput][2]*raspunde(step+1,nrstack-1,ppoz,true))%MOD;
else
{
if(step==n-1)
{
elim[cod(step,nrstack,ppoz,exista)]=true;
ma[cod(step,nrstack,ppoz,exista)]=1;
return 1;
}
long long q=putere(comb[n-ppoz][step+1-ppoz],MOD-2);
for(int newppoz=ppoz+1;newppoz<=step+2;++newppoz)
ans=(ans+comb[n-newppoz][step+2-newppoz]*q%MOD*comb[posibileInceput][2]%MOD*raspunde(step+1,nrstack-1,newppoz,false))%MOD;
}
}
if(posibileInceput&&ramas>=1)
ans=(ans+posibileInceput*ramas%MOD*raspunde(step+1,nrstack,ppoz,true))%MOD;
}
elim[cod(step,nrstack,ppoz,exista)]=true;
ma[cod(step,nrstack,ppoz,exista)]=ans;
return ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
factorial();
cin>>n;
for(int i=1;i<=n;++i)
cin>>v[i];
for(int i=0;i<=n;++i)
for(int j=0;j<=i;++j)
comb[i][j]=combinari(i,j);
cout<<raspunde(0,0,1,false);
return 0;
}
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
468 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
468 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
468 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
