Submission #796880

#	Time	Username	Problem	Language	Result	Execution time	Memory
796880		GusterGoose27	Festivals in JOI Kingdom 2 (JOI23_festival2)	C++17	37 / 100	1923 ms	468 KiB

festival2

#include <bits/stdc++.h>

using namespace std;

#define int long long

typedef long long ll;

int n, MOD;

const int MAXN = 31;

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

void free_endings(int i) { // how much stuff is left to allocate
	for (int j = 0; j <= n-i; j++) { // only this much stuff can actually exist
		for (int a = 0; a < 2; a++) {
			dp[i][j][a] = ((ll)dp[i][j][a]*facinv[j])%MOD + (j ? dp[i][j-1][a] : 0);
			dp[i][j][a] %= MOD;
		}
	}
	for (int j = 0; j <= n-i; j++) {
		for (int a = 0; a < 2; a++)
			dp[i][j][a] = ((ll)dp[i][j][a]*fac[j])%MOD;
	}
}

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);
}

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

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

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