#353577 (C++14) No.823 Many Shifts Easy

• 問題: No.823 Many Shifts Easy
• ユーザー: ahe100
• 提出日時: 2019-06-23 15:29:07
• 言語: C++14 (gcc 12.3.0 + boost 1.83.0)
• 結果: AC
• 実行時間: 3 ms / 2,000 ms
• コード長: 2,462 bytes
• コンパイル時間: 1,385 ms
• コンパイル使用メモリ: 170,524 KB
• 実行使用メモリ: 5,376 KB
• 最終ジャッジ日時: 2024-06-08 01:03:41
• 合計ジャッジ時間: 2,054 ms
• ジャッジサーバーID （参考情報）: judge5 / judge2

入力	結果	実行時間; 実行使用メモリ
testcase_00	AC	2 ms; 5,248 KB
testcase_01	AC	1 ms; 5,376 KB
testcase_02	AC	1 ms; 5,376 KB
testcase_03	AC	3 ms; 5,376 KB
testcase_04	AC	1 ms; 5,376 KB
testcase_05	AC	3 ms; 5,376 KB
testcase_06	AC	3 ms; 5,376 KB
testcase_07	AC	2 ms; 5,376 KB
testcase_08	AC	3 ms; 5,376 KB
testcase_09	AC	1 ms; 5,376 KB

ソースコード

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;

/*

*/

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;
	}
};
typedef ModInt<1000000007> mint;

vector<mint> fact, factinv;
void nCr_computeFactinv(int N) {
	N = min(N, mint::Mod - 1);
	fact.resize(N + 1); factinv.resize(N + 1);
	fact[0] = 1;
	reg(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 nCr(int n, int r) {
	if (n >= mint::Mod)
		return nCr(n % mint::Mod, r % mint::Mod) * nCr(n / mint::Mod, r / mint::Mod);
	return r > n ? 0 : fact[n] * factinv[n - r] * factinv[r];
}
mint nPr(int n, int r) {
	if (r<0)return 0;
	if (n >= mint::Mod)return nPr(n % mint::Mod, r % mint::Mod) * nPr(n / mint::Mod, r / mint::Mod);
	return r > n ? 0 : fact[n] * factinv[n-r];
}
mint nHr(int n, int r) { return r == 0 ? 1 : nCr(n + r - 1, r); }


ll N,K;
mint ans,n,k;

void init(){
	cin>>N>>K;
	n=N;
	k=K;
	nCr_computeFactinv(N);
}

int main(void){
	init();
	ans = n*(n+1)/2*nPr(N-1,K) + n*(n-1)/2*nCr(N-2,K-2)*fact[K]/2;
	cout<<ans.get()<<endl;
	return 0;
}