Submission #808681

#	Time	Username	Problem	Language	Result	Execution time	Memory
808681		starplat	Asceticism (JOI18_asceticism)	C++14	100 / 100	16 ms	2648 KiB

asceticism

#include <bits/stdc++.h>
#define int long long
const int mod=1e9+7LL;
using namespace std;
int n,k,fact[100005],inv[100005],invfact[100005],ans;
int fp(int x,int p){
	if (!p) return 1LL;
	int t=fp(x,p/2);
	t=(t*t)%mod;
	if (p&1LL) t*=x;
	return t%mod;
}
int ncr(int x,int p){
	return (fact[x]*invfact[p]%mod*invfact[x-p])%mod;
}
signed main(){
	cin>>n>>k;
	fact[0]=1LL;
	k=n-k;
	for (int i=1;i<=n+1;i++) fact[i]=(fact[i-1]*i)%mod;
	inv[1]=invfact[0]=invfact[1]=1LL;
	for (int i=2;i<=n+1;i++){
		inv[i]=mod-mod/i*inv[mod%i]%mod;
		invfact[i]=(invfact[i-1]*inv[i])%mod;
	}
	for (int i=0;i<=k;i++){
		int cal=ncr(n+1,i)*fp(k+1LL-i,n)%mod;
		if (i&1LL) ans+=(mod-cal);
		else ans+=cal;
		ans%=mod;
	}
	cout<<ans%mod<<"\n";
}

• Subtask 1: 4 / 4
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 51 / 51