Submission #10312260


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#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define all(x) (x).begin(),(x).end()
//#pragma GCC optimize ("-O3")
using namespace std; void _main(); int main() { cin.tie(0); ios::sync_with_stdio(false); _main(); }
typedef long long ll; const int inf = INT_MAX / 2; const ll infl = 1LL << 60;
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
//---------------------------------------------------------------------------------------------------
template<int MOD> struct ModInt {
    static const int Mod = MOD; unsigned x; ModInt() : x(0) { }
    ModInt(signed sig) { x = sig < 0 ? sig % MOD + MOD : sig % MOD; }
    ModInt(signed long long sig) { x = sig < 0 ? sig % MOD + MOD : sig % MOD; }
    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 { long long a = x, b = MOD, u = 1, v = 0;
        while (b) { long long t = a / b; a -= t * b; std::swap(a, b); u -= t * v; std::swap(u, v); }
        return ModInt(u); }
    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> ostream& operator<<(ostream& st, const ModInt<MOD> a) { st << a.get(); return st; };
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; }
template<typename T, int FAC_MAX> struct Comb { vector<T> fac, ifac;
    Comb(){fac.resize(FAC_MAX,1);ifac.resize(FAC_MAX,1);rep(i,1,FAC_MAX)fac[i]=fac[i-1]*i;
        ifac[FAC_MAX-1]=T(1)/fac[FAC_MAX-1];rrep(i,FAC_MAX-2,1)ifac[i]=ifac[i+1]*T(i+1);}
    T aPb(int a, int b) { if (b < 0 || a < b) return T(0); return fac[a] * ifac[a - b]; }
    T aCb(int a, int b) { if (b < 0 || a < b) return T(0); return fac[a] * ifac[a - b] * ifac[b]; }
    // nHk = (n+k-1)Ck : n is separator
    T nHk(int n, int k) { if (n == 0 && k == 0) return T(1); if (n <= 0 || k < 0) return 0;
        return aCb(n + k - 1, k); }
    T pairCombination(int n) {if(n%2==1)return T(0);return fac[n]*ifac[n/2]/(T(2)^(n/2));}
    // combination of paris for n
}; 
typedef ModInt<1000000007> mint;
/*---------------------------------------------------------------------------------------------------
            ∧_∧
      ∧_∧  (´<_` )  Welcome to My Coding Space!
     ( ´_ゝ`) /  ⌒i     @hamayanhamayan0
    /   \     | |
    /   / ̄ ̄ ̄ ̄/  |
  __(__ニつ/     _/ .| .|____
     \/____/ (u ⊃
---------------------------------------------------------------------------------------------------*/














int N, K;
Comb<mint, 401010> com;
//---------------------------------------------------------------------------------------------------
void _main() {
    cin >> N >> K;
    chmin(K, N - 1);

    mint ans = 0;
    rep(zero, 0, min(K + 1, N)) ans += com.aCb(N, zero) * com.nHk(N - zero, N - (N - zero));
    cout << ans << endl;
}





Submission Info

Submission Time
Task E - Roaming
User hamayanhamayan
Language C++14 (GCC 5.4.1)
Score 500
Code Size 4045 Byte
Status AC
Exec Time 10 ms
Memory 3456 KB

Judge Result

Set Name All Sample
Score / Max Score 500 / 500 0 / 0
Status
AC × 29
AC × 3
Set Name Test Cases
All sample_01.txt, sample_02.txt, sample_03.txt, testcase_1.txt, testcase_10.txt, testcase_11.txt, testcase_12.txt, testcase_13.txt, testcase_14.txt, testcase_15.txt, testcase_16.txt, testcase_17.txt, testcase_18.txt, testcase_19.txt, testcase_2.txt, testcase_20.txt, testcase_21.txt, testcase_22.txt, testcase_23.txt, testcase_24.txt, testcase_25.txt, testcase_26.txt, testcase_3.txt, testcase_4.txt, testcase_5.txt, testcase_6.txt, testcase_7.txt, testcase_8.txt, testcase_9.txt
Sample sample_01.txt, sample_02.txt, sample_03.txt
Case Name Status Exec Time Memory
sample_01.txt AC 8 ms 3456 KB
sample_02.txt AC 10 ms 3456 KB
sample_03.txt AC 7 ms 3456 KB
testcase_1.txt AC 7 ms 3456 KB
testcase_10.txt AC 8 ms 3456 KB
testcase_11.txt AC 8 ms 3456 KB
testcase_12.txt AC 8 ms 3456 KB
testcase_13.txt AC 8 ms 3456 KB
testcase_14.txt AC 8 ms 3456 KB
testcase_15.txt AC 8 ms 3456 KB
testcase_16.txt AC 8 ms 3456 KB
testcase_17.txt AC 10 ms 3456 KB
testcase_18.txt AC 9 ms 3456 KB
testcase_19.txt AC 8 ms 3456 KB
testcase_2.txt AC 7 ms 3456 KB
testcase_20.txt AC 9 ms 3456 KB
testcase_21.txt AC 8 ms 3456 KB
testcase_22.txt AC 8 ms 3456 KB
testcase_23.txt AC 8 ms 3456 KB
testcase_24.txt AC 8 ms 3456 KB
testcase_25.txt AC 8 ms 3456 KB
testcase_26.txt AC 9 ms 3456 KB
testcase_3.txt AC 10 ms 3456 KB
testcase_4.txt AC 10 ms 3456 KB
testcase_5.txt AC 10 ms 3456 KB
testcase_6.txt AC 10 ms 3456 KB
testcase_7.txt AC 10 ms 3456 KB
testcase_8.txt AC 7 ms 3456 KB
testcase_9.txt AC 8 ms 3456 KB