test/DPL_5_B.test.cpp

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Last update: 2020-11-27 17:14:27+09:00
Problem: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=DPL_5_B

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Code

#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=DPL_5_B"

#include "src/template.hpp"
#include "src/modint.hpp"
#include "src/combination.hpp"

int main() {
  ll n, k;
  cin >> n >> k;
  Combination<mint> c(max(n, k));
  cout << c.P(k, n) << el;
}

#line 1 "test/DPL_5_B.test.cpp"
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=DPL_5_B"

#line 2 "src/template.hpp"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pl = pair<ll, ll>;
using vl = vector<ll>;
#define rep(i, n) for(ll i = 0; i < (ll)n; i++)
#define rep3(i, l, r) for(ll i = l; i < (ll)r; i++)
#define per(i, n) for(ll i = (ll)n-1; i >= 0; i--)
#define per3(i, l, r) for(ll i = (ll)r-1; i >= (ll)l; i--)
#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)
template<class T, class U> inline void cmax(T &a, U b) { if (a < b) a = b; }
template<class T, class U> inline void cmin(T &a, U b) { if (a > b) a = b; }
constexpr char el = '\n';
template<class T, class U> ostream &operator<<(ostream &os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<class T, class U> istream &operator>>(istream &is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<class T> ostream &operator<<(ostream &os, const vector<T> &v) { rep(i, v.size()) os << v[i] << (i+1 != (ll)v.size() ? " " : ""); return os; }
template<class T> istream &operator>>(istream &is, vector<T> &v) { for(T &i : v) is >> i; return is; }
struct IoSetup {
  IoSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(15); }
} io_setup;
#line 3 "src/modint.hpp"

template <ll Mod>
struct ModInt {
  ll n;

  ModInt(const ll x = 0) : n(x) {
    while (n < 0) n += Mod;
    n %= Mod;
  }

  inline constexpr ModInt operator+(const ModInt r) const noexcept { return ModInt(*this) += r; }
  inline constexpr ModInt operator-(const ModInt r) const noexcept { return ModInt(*this) -= r; }
  inline constexpr ModInt operator*(const ModInt r) const noexcept { return ModInt(*this) *= r; }
  inline constexpr ModInt operator/(const ModInt r) const noexcept { return ModInt(*this) /= r; }
  inline constexpr ModInt &operator+=(const ModInt r) noexcept {
    n += r.n;
    if (n >= Mod) n -= Mod;
    return *this;
  }
  inline constexpr ModInt &operator-=(const ModInt r) noexcept {
    if (n < r.n) n += Mod;
    n -= r.n;
    return *this;
  }
  inline constexpr ModInt &operator*=(const ModInt r) noexcept {
    n = n * r.n % Mod;
    return *this;
  }
  inline constexpr ModInt &operator/=(const ModInt r) noexcept { return *this *= r.inv(); }

  inline constexpr ModInt pow(ll x) const noexcept {
    ModInt<Mod> ret(1), tmp(*this);
    while (x) {
      if (x&1) ret *= tmp;
      tmp *= tmp;
      x >>= 1;
    }
    return ret;
  }
  inline constexpr ModInt inv() const noexcept { return pow(Mod-2); }

  friend ostream& operator<<(ostream& os, const ModInt& obj) { return os << obj.n; }
  friend istream& operator>>(istream& is, ModInt& obj) {
    ll t;
    is >> t;
    obj = ModInt(t);
    return is;
  }
};

constexpr ll mod = 1000000007;
using mint = ModInt<mod>;
mint operator"" _mi(unsigned long long n) { return mint(n); }
#line 3 "src/combination.hpp"

// T modint
template<class T>
struct Combination {
  vector<T> fact, inv_fact;
  Combination(ll n) : fact(n+1), inv_fact(n+1) {
    fact[0] = T(1);
    for (ll i = 1; i <= n; i++) fact[i] = fact[i-1] * static_cast<T>(i);
    inv_fact[n] = fact[n].inv();
    for (ll i = n; i > 0; i--) inv_fact[i-1] = inv_fact[i] * static_cast<T>(i);
  }

  T P(ll n, ll k) const {
    if (n < k or k < 0) return T(0);
    return fact[n] * inv_fact[n-k];
  }

  T C(ll n, ll k) const {
    if (n < k or k < 0) return T(0);
    return fact[n] * inv_fact[n-k] * inv_fact[k];
  }

  T H(ll n, ll k) const {
    if (n < 0 or k < 0) return T(0);
    if (n == 0 and k == 0) return T(1);
    return C(n+k-1, n-1);
  }
};
#line 6 "test/DPL_5_B.test.cpp"

int main() {
  ll n, k;
  cin >> n >> k;
  Combination<mint> c(max(n, k));
  cout << c.P(k, n) << el;
}