Submission #853102

#	Time	Username	Problem	Language	Result	Execution time	Memory
853102		willychan	Festivals in JOI Kingdom 2 (JOI23_festival2)	C++14	87 / 100	9026 ms	1368 KiB

festival2

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
//#include<bits/extc++.h>
//__gnu_pbds
const int N = 20005;

int n;
int MOD;
ll fac[2*N];
ll invfac[2*N];

int fastpow(int a,ll p){
	int r = 1;	
	while(p){
		if(p&1)	r = (1LL*r*a)%MOD;
		a = (1LL*a*a)%MOD;
		p>>=1;
	}
	return r;
}

ll dp[N+2][2];
int main(){
	ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	cin>>n>>MOD;
	fac[0]=1;
	for(int i=1;i<=2*n+2;i++){
		fac[i] = (1LL*fac[i-1]*i)%MOD;
	}
	invfac[2*n+2] = fastpow(fac[2*n+2],MOD-2);
	invfac[0]=1;
	for(int i=2*n+1;i>=1;i--){
		invfac[i] = (1LL*invfac[i+1]*(i+1))%MOD;
	}
	dp[1][1]=1;
	dp[2][0]=1;
	for(int i=1;i<=n;i++){
		for(int f=0;f<2;f++){
		//	cout<<dp[i][f]<<" ";
			if(!dp[i][f]) continue;
			for(int t=0;t<2;t++){
				for(int j=0;i+j+1+!t<=n;j++){
					int k = dp[i][f];
					/*
					if(f==0 && t==0) k = 1LL*(1LL*k*(1LL*(j+1)*(j+2)%MOD)%MOD)*(fac[2*i-3+j]*invfac[2*i-3]%MOD)%MOD;
					if(f==0 && t==1) k = 1LL*(1LL*k*(j+1)%MOD)*(fac[2*i-3+j]*invfac[2*i-3]%MOD)%MOD;
					if(f==1 && t==0) k = 1LL*(1LL*k*(1LL*(j+1)%MOD)%MOD)*(fac[2*i-2+j]*invfac[2*i-2]%MOD)%MOD;
					if(f==1 && t==1) k = 1LL*(1LL*k)*(fac[2*i-2+j]*invfac[2*i-2]%MOD)%MOD;
					*/
					if(!f || !t) k = 1LL*k*(j+1)%MOD;
					if(!f && !t) k = 1LL*k*(j+2)%MOD;
					k = (1LL*k*(fac[2*i-3+j+f]*invfac[2*i-3+f]%MOD))%MOD;
					dp[i+j+1+(!t)][t] +=k;
					dp[i+j+1+(!t)][t] -=(dp[i+j+1+(!t)][t]>=MOD)?(MOD):(0);
				}
			}
		}
		//cout<<"\n";
	}
	
	ll total = (1LL*fac[2*n]*invfac[n])%MOD;
	total = (1LL*total*fastpow(invfac[2],n))%MOD;
	
	//ll total=1;
	//for(int i=1;i<=n;i++) total = 1LL*total*(2*n-2*i+1)%MOD;
	for(int i=1;i<=n;i++){
		
		if(dp[i][0]) total = (total-(1LL*dp[i][0]*(n-i+1)%MOD*fac[i+n-3]%MOD*invfac[2*i-3]%MOD))%MOD;
		if(dp[i][1]) total = (total-(1LL*dp[i][1]*fac[i+n-2]%MOD*invfac[2*i-2]%MOD))%MOD;
		//cout<<total<<"\n";
	}
	if(total<0) total+=MOD;
	cout<<total<<"\n";
	return 0;
}



/*
dp[i][0]*fac[2*i+j-3]*invfac[2*i-3]*(j+2)*(j+1)*invfac[2] =+> dp[i+j+2][0]
dp[i][0]* =+> dp[i+j+1][1]
dp[i][1] =+> dp[i+j+2][0]
dp[i][1] =+>. dp[i+j+1][1]



*/

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 27 / 27
• Subtask 4: 14 / 14
• Subtask 5: 36 / 36
• Subtask 6: 0 / 13