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ID题目提交者结果用时内存语言文件大小提交时间测评时间
#65820#4843. Infectious Diseaseclf123456TL 182ms239048kbC++201.4kb2022-12-03 18:40:562022-12-03 18:40:57

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 18:40:57]
  • 评测
  • 测评结果:TL
  • 用时:182ms
  • 内存:239048kb
  • [2022-12-03 18:40:56]
  • 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;
int mp[maxn];
struct hash_map{
	bool operator()(const pair<int,int>& p) const{
		return p.first+mp[p.second]*maxn;
	}
};
unordered_map<pair<int,int>,int,hash_map>dp;


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;
	pair<int,int>t=make_pair(x,y);
	if(dp.find(t)!=dp.end()) return dp[t];
	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[t]=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;
		//cout<<base<<" "<<mp[base]<<endl;
		base*=3;
		
	}
}
signed main(){
	//memset(dp,-1,sizeof(dp));
	cin>>n;
	init();
	
	int base=1;
	
	cout<<dfs(1,1)<<endl;
	return 0;
} 

详细

Test #1:

score: 100
Accepted
time: 166ms
memory: 238772kb

input:

2

output:

1

result:

ok 1 number(s): "1"

Test #2:

score: 0
Accepted
time: 182ms
memory: 239048kb

input:

114

output:

505208013

result:

ok 1 number(s): "505208013"

Test #3:

score: -100
Time Limit Exceeded

input:

14000000

output:


result: