Submission #46777

#	Time	Username	Problem	Language	Result	Execution time	Memory
46777		kyleliu	Asceticism (JOI18_asceticism)	C++14	100 / 100	30 ms	2440 KiB

asceticism

#include <bits/stdc++.h> // PLEASE

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair <int, int> pp;
#define MAXN 100005
#define MAXM 1005
#define MAXP 25
#define A first
#define B second
#define MP make_pair
#define PB push_back
const ll INF = 2e9+13;
const ll MOD = 1e9+7;
int N, K;
ll fac[MAXN]; ll ifa[MAXN];
ll mmul(ll a, ll b) { return (a*b)%MOD; }
ll madd(ll a, ll b) { return (a+b)%MOD; }
ll nck(ll n, ll k)
{	
	return mmul(fac[n], mmul(ifa[n-k], ifa[k]));
}

ll pmod(ll a, ll b)
{
	ll ret = 1LL;
	while(b) {
		if(b & 1) ret = mmul(ret, a);
		a = mmul(a, a);
		b /= 2LL;
	}
	return ret;
}

ll euler(ll n, ll m)
{
	ll ans = 0;
	for(int k=0; k<=m+1; k++) {
		ll add = nck(n+1, k);
		add = mmul(add, pmod(m+1-k, n));
		if(k%2) ans = madd(ans, MOD-add);
		else ans = madd(ans, add);
	}
	return ans; 
}
int main(void)
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	fac[0] = 1LL; ifa[0] = 1LL;
	for(int i=1; i<MAXN; i++) {
		fac[i] = mmul(fac[i-1], i);
		ifa[i] = pmod(fac[i], MOD-2);
	}
	
	cin >> N >> K;
	cout << euler(N, N-K) << endl;
}

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