QOJ.ac

QOJ

IDProblemSubmitterResultTimeMemoryLanguageFile sizeSubmit timeJudge time
#65743#4843. Infectious Diseaseclf123456ML 0ms0kbC++141.1kb2022-12-03 16:23:342022-12-03 16:23:34

Judging History

你现在查看的是最新测评结果

  • [2023-08-10 23:21:45]
  • System Update: QOJ starts to keep a history of the judgings of all the submissions.
  • [2022-12-03 16:23:34]
  • 评测
  • 测评结果:ML
  • 用时:0ms
  • 内存:0kb
  • [2022-12-03 16:23:34]
  • 提交

answer

#include<bits/stdc++.h>
#define int long long

using namespace std;
const int maxn=1e7+5e6;
const int mod=1e9+7;
int jc[maxn],inv[maxn],n;
signed dp[maxn][16];
int mp[maxn];
int C(int n,int m){
	return jc[n]*inv[n-m]%mod*inv[m]%mod;
}
int ksm(int x,int p,int mod){
	int ans=1;
	while(p){
		if(p&1) ans=ans*x%mod;
		x=x*x%mod;
		p>>=1;
	}
	return ans;
}
int dfs(int x,int y){
	if(x==0) return 0;
	if(dp[x][y]!=-1) return dp[x][y];
	int r=min(2*x,n-y);
	int z=min(2*y,n-y);
	int sum=n-y;
	int mn=max(0LL,r+z-sum);
	int mx=min(r,z);
	int ans=1;
	int fm=ksm(C(n-y,z),mod-2,mod);
	for(int i=mn;i<=mx;i++){
		ans+=C(r,i)*C(n-y-r,z-i)%mod*dfs(r-i,z+y)%mod*fm%mod;
		ans%=mod;
	}
	return dp[x][y]=ans;
}
void init(){
	jc[0]=inv[0]=1;
	for(int i=1;i<maxn;i++) jc[i]=i*jc[i-1]%mod;
	inv[maxn-1]=ksm(jc[maxn-1],mod-2,mod);
	for(int i=maxn-2;i>=1;i--){
		inv[i]=(i+1)*inv[i+1]%mod;
	}
	mp[1]=0;
	int base=3;
	for(int i=1;;i++){
		if(base>=n){
			mp[n]=i;
			break;
		}
		mp[base]=i;
		base*=3;
		
	}
}
signed main(){
	memset(dp,-1,sizeof(dp));
	init();
	int base=1;
	cin>>n;
	cout<<dfs(1,1)<<endl;
	return 0;
} 

Details

Tip: Click on the bar to expand more detailed information

Test #1:

score: 0
Memory Limit Exceeded

input:

2

output:


result: