Submission #796977

#	Time	Username	Problem	Language	Result	Execution time	Memory
796977		GusterGoose27	Festivals in JOI Kingdom 2 (JOI23_festival2)	C++17	87 / 100	9060 ms	920 KiB

festival2

#pragma GCC optimize("Ofast,unroll-loops")

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

int n, MOD;

const int MAXN = 20005;

int dp[MAXN][2];
int fac[3*MAXN];
int facinv[3*MAXN];

int expo(ll a, int b) {
	ll cur = 1;
	while (b) {
		if (b & 1) {
			cur = (cur*a)%MOD;
		}
		a = (a*a)%MOD;
		b /= 2;
	}
	return cur;
}

int inv(int a) {
	return expo(a, MOD-2);
}

int choose(int a, int b) {
	ll cur = (ll)fac[a]*facinv[b];
	cur %= MOD;
	return (cur*facinv[a-b])%MOD;
}

void fastmod(int &a) {
	if (a > MOD) a -= MOD;
}

int main() {
	cin >> n >> MOD;
	fac[0] = facinv[0] = 1;
	for (int i = 1; i <= 3*n; i++) {
		fac[i] = ((ll)i*fac[i-1])%MOD;
	}
	facinv[3*n] = inv(fac[3*n]);
	for (int i = 3*n-1; i > 0; i--) {
		facinv[i] = ((ll)(i+1)*facinv[i+1])%MOD;
	}
	dp[0][0] = dp[0][1] = 1;
	// for (int i = 0; i <= n; i++) {
	// 	dp[0][0] = fac[i];
	// 	dp[0][1] = fac[i+1];
	// }
	for (int i = 1; i <= n; i++) {
		for (int a = 0; a <= i-1; a++) {
			for (int t2 = 0; t2 < 2; t2++) {
				if (t2 && a == i-1) continue; // factorial of 
				ll cur = (ll)dp[i-a-1-t2][t2]*fac[a+t2];;
				cur %= MOD;
				cur *= choose(2*i-a-t2-2, a); cur %= MOD;
				// if (i == 2 && t1 == 0) cerr << cur << '\n';
				dp[i][0] += cur;
				fastmod(dp[i][0]);
				dp[i][1] += (cur*(a+1+t2))%MOD;
				fastmod(dp[i][1]);
			}
		}
	}
	ll oth = 1;
	for (int i = 2*n-1; i > 0; i -= 2) {
		oth = (oth*i)%MOD;
	}
	cout << (oth+MOD-dp[n][0])%MOD << '\n';
}

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