Submission #163510

#	Time	Username	Problem	Language	Result	Execution time	Memory
163510		iefnah06	Asceticism (JOI18_asceticism)	C++11	100 / 100	14 ms	1400 KiB

asceticism

#include<bits/stdc++.h>
using namespace std;

template <int MOD_>
struct modnum {
	static constexpr int MOD = MOD_;
	static_assert(MOD_ > 0, "MOD must be positive");
 
private:
	using ll = long long;
 
	int v;
 
	static int minv(int a, int m) {
		a %= m;
		assert(a);
		return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
	}
 
public:
 
	modnum() : v(0) {}
	modnum(ll v_) : v(int(v_ % MOD)) { if (v < 0) v += MOD; }
	explicit operator int() const { return v; }
	friend std::ostream& operator << (std::ostream& out, const modnum& n) { return out << int(n); }
	friend std::istream& operator >> (std::istream& in, modnum& n) { ll v_; in >> v_; n = modnum(v_); return in; }
 
	friend bool operator == (const modnum& a, const modnum& b) { return a.v == b.v; }
	friend bool operator != (const modnum& a, const modnum& b) { return a.v != b.v; }
 
	modnum inv() const {
		modnum res;
		res.v = minv(v, MOD);
		return res;
	}
	modnum neg() const {
		modnum res;
		res.v = v ? MOD-v : 0;
		return res;
	}
 
	modnum operator- () const {
		return neg();
	}
	modnum operator+ () const {
		return modnum(*this);
	}
 
	modnum& operator ++ () {
		v ++;
		if (v == MOD) v = 0;
		return *this;
	}
	modnum& operator -- () {
		if (v == 0) v = MOD;
		v --;
		return *this;
	}
	modnum& operator += (const modnum& o) {
		v += o.v;
		if (v >= MOD) v -= MOD;
		return *this;
	}
	modnum& operator -= (const modnum& o) {
		v -= o.v;
		if (v < 0) v += MOD;
		return *this;
	}
	modnum& operator *= (const modnum& o) {
		v = int(ll(v) * ll(o.v) % MOD);
		return *this;
	}
	modnum& operator /= (const modnum& o) {
		return *this *= o.inv();
	}
 
	friend modnum operator ++ (modnum& a, int) { modnum r = a; ++a; return r; }
	friend modnum operator -- (modnum& a, int) { modnum r = a; --a; return r; }
	friend modnum operator + (const modnum& a, const modnum& b) { return modnum(a) += b; }
	friend modnum operator - (const modnum& a, const modnum& b) { return modnum(a) -= b; }
	friend modnum operator * (const modnum& a, const modnum& b) { return modnum(a) *= b; }
	friend modnum operator / (const modnum& a, const modnum& b) { return modnum(a) /= b; }
};
using num = modnum<int(1e9) + 7>;

num powmod(num a, int b) {
	num r = 1;
	while (b) {
		if (b & 1) {
			r *= a;
		}
		a *= a;
		b /= 2;
	}
	return r;
}

const int MAXN = 1.1e5;
int N, K;

num fact[MAXN];
num ifact[MAXN];
num choose(int n, int r) {
	return fact[n] * ifact[r] * ifact[n-r];
}

int main() {
	fact[0] = 1;
	for (int i = 1; i < MAXN; i++) {
		fact[i] = fact[i-1] * i;
	}
	ifact[MAXN-1] = fact[MAXN-1].inv();
	for (int i = MAXN-1; i >= 1; i--) {
		ifact[i-1] = ifact[i] * i;
	}

	cin >> N >> K;
	num ans = 0;
	for (int c = 0; c < K; c++) {
		num ways = choose(N+1, c) * powmod(K-c, N);
		if (c % 2 == 0) {
			ans += ways;
		} else {
			ans -= ways;
		}
	}
	cout << ans << '\n';

	return 0;
}

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