#990658 (C++17) No.2791 Beginner Contest

• 問題: No.2791 Beginner Contest
• ユーザー: tnakao0123
• 提出日時: 2024-06-24 18:15:55
• 言語: C++17 (gcc 13.3.0 + boost 1.87.0)
• 結果: AC
• 実行時間: 39 ms / 2,000 ms
• コード長: 1,947 bytes
• コンパイル時間: 446 ms
• コンパイル使用メモリ: 57,052 KB
• 最終ジャッジ日時: 2025-02-22 00:19:24
• ジャッジサーバーID （参考情報）: judge3 / judge2

ファイルパターン	結果
sample	AC * 3
other	AC * 17

コンパイルメッセージ

main.cpp: In function ‘int main()’:
main.cpp:81:8: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   81 |   scanf("%d%d", &n, &k);
      |   ~~~~~^~~~~~~~~~~~~~~~

ソースコード

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/* -*- coding: utf-8 -*-
 *
 * 2791.cc:  No.2791 Beginner Contest - yukicoder
 */
#include<cstdio>
#include<vector>
#include<algorithm>
using namespace std;
/* constant */
const int MAX_N = 100000;
const int MOD = 998244353;
/* typedef */
template<const int MOD>
struct MI {
  int v;
  MI(): v() {}
  MI(int _v): v(_v % MOD) { if (v < 0) v += MOD; }
  MI(long long _v): v(_v % MOD) { if (v < 0) v += MOD; }
  explicit operator int() const { return v; }
  
  MI operator+(const MI m) const { return MI(v + m.v); }
  MI operator-(const MI m) const { return MI(v + MOD - m.v); }
  MI operator*(const MI m) const { return MI((long long)v * m.v); }
  MI &operator+=(const MI m) { return (*this = *this + m); }
  MI &operator-=(const MI m) { return (*this = *this - m); }
  MI &operator*=(const MI m) { return (*this = *this * m); }
  bool operator==(const MI m) const { return v == m.v; }
  bool operator!=(const MI m) const { return v != m.v; }
  MI pow(int n) const {  // a^n % MOD
    MI pm = 1, a = *this;
    while (n > 0) {
      if (n & 1) pm *= a;
      a *= a;
      n >>= 1;
    }
    return pm;
  }
  MI inv() const { return pow(MOD - 2); }
  MI operator/(const MI m) const { return *this * m.inv(); }
  MI &operator/=(const MI m) { return (*this = *this / m); }
};
using mi = MI<MOD>;
using vmi = vector<mi>;
/* global variables */
vmi fs, invfs;
/* subroutines */
inline mi nck(int n, int k) {  // nCk % MOD
  if (n < k || k < 0) return 0;
  return fs[n] * invfs[n - k] * invfs[k];
}
void prepare_fracs(int n) {
  fs.resize(n + 1), invfs.resize(n + 1);
  fs[0] = invfs[0] = 1;
  for (int i = 1; i <= n; i++) {
    fs[i] = fs[i - 1] * i;
    invfs[i] = fs[i].inv();
  }
}
/* main */
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  prepare_fracs(n * 2);
  
  mi sum = 1;
  for (int i = 1; i <= n && i * k <= n; i++) {
    int m = n - i * k;
    sum += nck(m + i, i);
  }
  printf("%d\n", (int)sum);
  
  return 0;
}
 
 
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