結果

問題 No.391 CODING WAR
コンテスト
ユーザー frmon60
提出日時 2019-09-08 23:34:05
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 23 ms / 2,000 ms
コード長 2,889 bytes
コンパイル時間 1,638 ms
コンパイル使用メモリ 170,188 KB
実行使用メモリ 5,376 KB
最終ジャッジ日時 2024-06-27 15:18:06
合計ジャッジ時間 2,805 ms
ジャッジサーバーID
（参考情報） 		judge5 / judge1
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ファイルパターン 結果
sample AC * 4
other AC * 16
権限があれば一括ダウンロードができます

ソースコード

diff # 

#include <bits/stdc++.h>
using namespace std;
using Int = long long;
typedef pair<int,int> P; typedef priority_queue<int> Pr; typedef vector<int> V; typedef vector<P> Vp; typedef map<int,int> MP;
const int mod = 1000000007; const Int INF = 1145141919810893931;
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define END cout<<ans<<'\n'; return 0;
template<class T> inline bool cmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool cmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<int MOD>
struct ModInt {
	static const int Mod = MOD;
	unsigned x;
	ModInt() : x(0) {}
	ModInt(signed sig) { int sigt = sig % MOD; if(sigt < 0) sigt += MOD; x = sigt; }
	ModInt(signed long long sig) { int sigt = sig % MOD; if(sigt < 0) sigt += MOD; x = sigt; }
	int get() const { return (int)x; }

	ModInt &operator+=(ModInt that) { if((x += that.x) >= MOD) x -= MOD; return *this; }
	ModInt &operator-=(ModInt that) { if((x += MOD - that.x) >= MOD) x -= MOD; return *this; }
	ModInt &operator*=(ModInt that) { x = (unsigned long long)x * that.x % MOD; return *this; }
	ModInt &operator/=(ModInt that) { return *this *= that.inverse(); }

	ModInt operator+(ModInt that) const { return ModInt(*this) += that; }
	ModInt operator-(ModInt that) const { return ModInt(*this) -= that; }
	ModInt operator*(ModInt that) const { return ModInt(*this) *= that; }
	ModInt operator/(ModInt that) const { return ModInt(*this) /= that; }

	ModInt inverse() const {
		signed a = x, b = MOD, u = 1, v = 0;
		while(b) {
			signed t = a / b;
			a -= t * b; std::swap(a, b);
			u -= t * v; std::swap(u, v);
		}
		if(u < 0) u += Mod;
		ModInt res; res.x = (unsigned)u;
		return res;
	}

	bool operator==(ModInt that) const { return x == that.x; }
	bool operator!=(ModInt that) const { return x != that.x; }
	ModInt operator-() const { ModInt t; t.x = x == 0 ? 0 : Mod - x; return t; }
};
template<int MOD> ModInt<MOD> operator^(ModInt<MOD> a, unsigned long long k) {
	ModInt<MOD> r = 1;
	while(k) {
		if(k & 1) r *= a;
		a *= a;
		k >>= 1;
	}
	return r;
}
typedef ModInt<mod> mint;
vector<mint> fact, factinv;

void COMinit(int N) {
	N = min(N, mint::Mod - 1);
	fact.resize(N + 1); factinv.resize(N + 1);
	fact[0] = 1;
	rer(i, 1, N) fact[i] = fact[i - 1] * i;
	factinv[N] = fact[N].inverse();
	for(int i = N; i >= 1; i --) factinv[i - 1] = factinv[i] * i;
}

mint C(int n, int r) {
	if(n >= mint::Mod)
		return C(n % mint::Mod, r % mint::Mod) * C(n / mint::Mod, r / mint::Mod);
	return r > n ? 0 : fact[n] * factinv[n - r] * factinv[r];
}

int main(){
    cin.tie(nullptr); ios::sync_with_stdio(false);

    Int n,k; mint ans=0; cin>>n>>k;
    if(n<k){cout<<ans.get()<<'\n'; return 0;}
    COMinit(200000);
    for (Int i = 0; i < k; i++){
        mint c=C(k,i)*(mint(k-i)^n);
        if(i%2)ans-=c;
        else ans+=c;
    }
    cout<<ans.get()<<'\n';
}
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