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#define PROBLEM "https://onlinejudge.u-aizu.ac.jp/courses/library/7/DPL/5/DPL_5_F" #include <bits/stdc++.h> // clang-format off using Int = long long; #define REP_(i, a_, b_, a, b, ...) for (Int i = (a), lim##i = (b); i < lim##i; i++) #define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__) struct SetupIO { SetupIO() { std::cin.tie(nullptr), std::ios::sync_with_stdio(false), std::cout << std::fixed << std::setprecision(13); } } setup_io; #ifndef _MY_DEBUG #define dump(...) #endif // clang-format on /** * author: knshnb * created: Sun Apr 12 17:57:28 JST 2020 **/ #define CALL_FROM_TEST #include "../../src/Math/Combination.hpp" #include "../../src/Math/ModInt.hpp" #undef CALL_FROM_TEST using mint = ModInt<1000000007>; signed main() { Int n, k; std::cin >> n >> k; Combination<mint> comb(n + k - 1); std::cout << (n < k ? 0 : comb(n - 1, k - 1)) << std::endl; }
#line 1 "test/aoj/DPL_5_F.test.cpp" #define PROBLEM "https://onlinejudge.u-aizu.ac.jp/courses/library/7/DPL/5/DPL_5_F" #include <bits/stdc++.h> // clang-format off using Int = long long; #define REP_(i, a_, b_, a, b, ...) for (Int i = (a), lim##i = (b); i < lim##i; i++) #define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__) struct SetupIO { SetupIO() { std::cin.tie(nullptr), std::ios::sync_with_stdio(false), std::cout << std::fixed << std::setprecision(13); } } setup_io; #ifndef _MY_DEBUG #define dump(...) #endif // clang-format on /** * author: knshnb * created: Sun Apr 12 17:57:28 JST 2020 **/ #define CALL_FROM_TEST #line 1 "src/Math/Combination.hpp" template <class T> struct Combination { std::vector<T> fact, fact_inv; Combination(int n = 1000003) : fact(n + 1, 1), fact_inv(n + 1) { for (int i = 0; i < n; i++) fact[i + 1] = fact[i] * (i + 1); fact_inv[n] = (T)1 / fact[n]; for (int i = n - 1; i >= 0; i--) fact_inv[i] = fact_inv[i + 1] * (i + 1); // for (int i = 0; i < n + 1; i++) assert(fact[i] * fact_inv[i] == 1); } T operator()(int n, int r) { return fact[n] * fact_inv[r] * fact_inv[n - r]; } }; #line 1 "src/Math/ModInt.hpp" template <class T> T pow(T x, long long n, const T UNION = 1) { T ret = UNION; while (n) { if (n & 1) ret *= x; x *= x; n >>= 1; } return ret; } /// @docs src/Math/ModInt.md template <int Mod> struct ModInt { int x; static int& runtime_mod() { static int runtime_mod_; return runtime_mod_; } // テンプレート引数が負のときは実行時ModInt static constexpr int mod() { return Mod < 0 ? runtime_mod() : Mod; } static std::unordered_map<int, int>& to_inv() { static std::unordered_map<int, int> to_inv_; return to_inv_; } static void set_runtime_mod(int mod) { static_assert(Mod < 0, "template parameter Mod must be negative for runtime ModInt"); runtime_mod() = mod, to_inv().clear(); } ModInt() : x(0) {} ModInt(long long x_) { if ((x = x_ % mod() + mod()) >= mod()) x -= mod(); } ModInt& operator+=(ModInt rhs) { if ((x += rhs.x) >= mod()) x -= mod(); return *this; } ModInt& operator*=(ModInt rhs) { x = (unsigned long long)x * rhs.x % mod(); return *this; } ModInt& operator-=(ModInt rhs) { if ((x -= rhs.x) < 0) x += mod(); return *this; } ModInt& operator/=(ModInt rhs) { ModInt inv = to_inv().count(rhs.x) ? to_inv()[rhs.x] : (to_inv()[rhs.x] = pow(rhs, mod() - 2).x); return *this *= inv; } ModInt operator-() const { return -x < 0 ? mod() - x : -x; } ModInt operator+(ModInt rhs) const { return ModInt(*this) += rhs; } ModInt operator*(ModInt rhs) const { return ModInt(*this) *= rhs; } ModInt operator-(ModInt rhs) const { return ModInt(*this) -= rhs; } ModInt operator/(ModInt rhs) const { return ModInt(*this) /= rhs; } bool operator==(ModInt rhs) const { return x == rhs.x; } bool operator!=(ModInt rhs) const { return x != rhs.x; } // 計算結果をmapに保存するべき乗 ModInt save_pow(int n) const { static std::map<std::pair<int, int>, int> tbl_pow; if (tbl_pow.count({x, n})) return tbl_pow[{x, n}]; if (n == 0) return 1; if (n % 2) return tbl_pow[{x, n}] = (*this * save_pow(n - 1)).x; return tbl_pow[{x, n}] = (save_pow(n / 2) * save_pow(n / 2)).x; } // 1 + r + r^2 + ... + r^(n-1)を逆元がない(modが素数でない)場合に計算 static ModInt geometric_progression(ModInt r, int n) { if (n == 0) return 0; if (n % 2) return geometric_progression(r, n - 1) + r.save_pow(n - 1); return geometric_progression(r, n / 2) * (r.save_pow(n / 2) + 1); } // a + r * (a - d) + r^2 * (a - 2d) + ... + r^(n-1) * (a - (n - 1)d) static ModInt linear_sum(ModInt r, ModInt a, ModInt d, int n) { if (n == 0) return 0; if (n % 2) return linear_sum(r, a, d, n - 1) + r.save_pow(n - 1) * (a - d * (n - 1)); return linear_sum(r, a, d, n / 2) * (r.save_pow(n / 2) + 1) - d * (n / 2) * r.save_pow(n / 2) * geometric_progression(r, n / 2); } friend std::ostream& operator<<(std::ostream& s, ModInt<Mod> a) { return s << a.x; } friend std::istream& operator>>(std::istream& s, ModInt<Mod>& a) { long long tmp; s >> tmp; a = ModInt<Mod>(tmp); return s; } friend std::string to_string(ModInt<Mod> a) { return std::to_string(a.x); } }; #ifndef CALL_FROM_TEST using mint = ModInt<1000000007>; #endif #line 20 "test/aoj/DPL_5_F.test.cpp" #undef CALL_FROM_TEST using mint = ModInt<1000000007>; signed main() { Int n, k; std::cin >> n >> k; Combination<mint> comb(n + k - 1); std::cout << (n < k ? 0 : comb(n - 1, k - 1)) << std::endl; }