Submission #246388

#	Time	Username	Problem	Language	Result	Execution time	Memory
246388		wwdd	Asceticism (JOI18_asceticism)	C++14	100 / 100	47 ms	2808 KiB

asceticism

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MN = 100100;
const ll M = 1e9+7;
inline ll mul(ll a, ll b) {return (a*b)%M;}
ll bp(ll b, ll p) {
	ll ac = 1;
	while(p) {
		if(p&1) {ac = mul(ac,b);}
		b = mul(b,b);
		p >>= 1;
	}
	return ac;
}
inline ll inv(ll v) {return bp(v,M-2);}
ll fp[MN];
ll fac(ll n) {
	if(n <= 1) {return 1;}
	if(fp[n] != -1) {return fp[n];}
	return fp[n] = mul(fac(n-1),n);
}
ll ch(ll n, ll k) {
	if(k < 0 || k > n) {return 0;}
	if(k <= 0 || k >= n) {return 1;}
	return mul(mul(fac(n),inv(fac(k))),inv(fac(n-k)));
}
int main() {
	memset(fp,-1,sizeof(fp));
	ll n,k;
	cin >> n >> k;
	ll res = 0;
	for(int i=0;i<k;i++) {
		ll sgn = (i&1)?-1:1;
		res += sgn*mul(bp(k-i,n),ch(n+1,i));
	}
	res = ((res%M)+M)%M;
	cout << res << '\n';
}

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