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QOJ
ID | Problem | Submitter | Result | Time | Memory | Language | File size | Submit time | Judge time |
---|---|---|---|---|---|---|---|---|---|
#65809 | #4843. Infectious Disease | clf123456 | TL | 172ms | 238308kb | C++20 | 1.4kb | 2022-12-03 18:20:00 | 2022-12-03 18:20:04 |
Judging History
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 pair_hash
{
bool operator() (const pair<int, int>& p) const
{
int h1 = (p.first);
int h2 = mp[p.second];
return h1 + h2 * maxn;
}
};
unordered_map<pair<int, int>, int, pair_hash> 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;
base*=3;
}
}
signed main(){
//memset(dp,-1,sizeof(dp));
init();
int base=1;
cin>>n;
cout<<dfs(1,1)<<endl;
return 0;
}
Details
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Test #1:
score: 100
Accepted
time: 172ms
memory: 237728kb
input:
2
output:
1
result:
ok 1 number(s): "1"
Test #2:
score: 0
Accepted
time: 159ms
memory: 238308kb
input:
114
output:
505208013
result:
ok 1 number(s): "505208013"
Test #3:
score: -100
Time Limit Exceeded
input:
14000000