제출 #551819

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
551819		Hanksburger	Tents (JOI18_tents)	C++17	100 / 100	110 ms	71088 KiB

tents

#include <bits/stdc++.h>
using namespace std;
const long long mod=1000000007, half=500000004;
long long dp[3005][3005], fac[3005], invfac[3005], invpow[3005];
long long power(long long a, long long b)
{
	if (!b)
		return 1;
	long long res=power(a, b/2);
	if (b&1)
		return res*res%mod*a%mod;
	else
		return res*res%mod;
}
long long nCr(long long n, long long r)
{
	return fac[n]*invfac[r]%mod*invfac[n-r]%mod;
}
int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	fac[0]=1;
	for (long long i=1; i<=3000; i++)
		fac[i]=fac[i-1]*i%mod;
	invfac[3000]=power(fac[3000], mod-2);
	for (long long i=2999; i>=0; i--)
		invfac[i]=invfac[i+1]*(i+1)%mod;
	invpow[0]=1;
	for (long long i=1; i<=3000; i++)
		invpow[i]=invpow[i-1]*half%mod;
	for (long long i=0; i<=3000; i++)
		dp[0][i]=1;
	for (long long i=1; i<=3000; i++)
		dp[i][0]=1;
	for (long long i=1; i<=3000; i++)
		for (long long j=1; j<=3000; j++)
			dp[i][j]=(dp[i-1][j-1]*j*4+dp[i-1][j])%mod;
	long long n, m, ans=0;
	cin >> n >> m;
	for (long long i=0; i<=min(n, m/2); i++)
	{
		for (long long j=0; j<=min((n-i)/2, m-i*2); j++)
		{
			long long num1=nCr(n, i);
			long long num2=fac[m]*invfac[m-i*2]%mod*invpow[i]%mod;
			long long num3=nCr(m-i*2, j);
			long long num4=fac[n-i]*invfac[n-i-j*2]%mod*invpow[j]%mod;
			ans=(ans+num1*num2%mod*num3%mod*num4%mod*dp[n-i-j*2][m-i*2-j])%mod;
		}
	}
	cout << ans-1;
	return 0;
}

• Subtask 1: 48 / 48
• Subtask 2: 52 / 52