Submission #696514

#	Time	Username	Problem	Language	Result	Execution time	Memory
696514		lucri	Ruins 3 (JOI20_ruins3)	C++17	0 / 100	6043 ms	340 KiB

ruins3

#include <bits/stdc++.h>
#define MOD  1000000007
using namespace std;
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];
void factorial()
{
    fact[0]=1;
    for(long long i=1;i<=600;++i)
        fact[i]=fact[i-1]*i%MOD;
}
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];
long long raspunde(long long step,long long nrstack,long long ppoz,bool exista)
{
    if(step==n)
        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+combinari(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+combinari(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)
                return 1;
            if(ramas-1)
                ans=(ans+posibileInceput*(ramas-1)%MOD*raspunde(step+1,nrstack,ppoz,false))%MOD;
            long long q=putere(combinari(n-ppoz,step+1-ppoz),MOD-2);
            for(int newppoz=ppoz+1;newppoz<=step+2;++newppoz)
                ans=(ans+combinari(n-newppoz,step+2-newppoz)*q%MOD*posibileInceput%MOD*raspunde(step+1,nrstack,newppoz,false))%MOD;
        }
    }
    else
    {
        if(ramas>=2)
            ans=(ans+combinari(ramas,2)*raspunde(step+1,nrstack+1,ppoz,true))%MOD;
        if(posibileInceput>=2)
        {
            if(nrstack>=2)
                ans=(ans+combinari(posibileInceput,2)*raspunde(step+1,nrstack-1,ppoz,true))%MOD;
            else
            {
                if(step==n-1)
                    return 1;
                long long q=putere(combinari(n-ppoz,step+1-ppoz),MOD-2);
                for(int newppoz=ppoz+1;newppoz<=step+2;++newppoz)
                    ans=(ans+combinari(n-newppoz,step+2-newppoz)*q%MOD*combinari(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;
    }
    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];
    cout<<raspunde(0,0,1,false);
    return 0;
}

• Subtask 1: 0 / 6
• Subtask 2: 0 / 52
• Subtask 3: 0 / 42