Submission #1252085

#	Time	Username	Problem	Language	Result	Execution time	Memory
1252085		LucaLucaM	Asceticism (JOI18_asceticism)	C++20	100 / 100	9 ms	1096 KiB

asceticism

#include <iostream>
#include <vector>
#include <algorithm>
#include <cassert>

using ll = long long;
#define debug(x) #x << " = " << x << '\n'

const int mod = 1e9 + 7;
const int MAXN = 1e5;

int fac[MAXN + 2];
int ifac[MAXN + 2];

int power(int a, int b) {
  int ret = 1;
  while (b) {
    if (b & 1) {
      ret = (ll) ret * a % mod;
    }
    a = (ll) a * a % mod;
    b >>= 1;
  }
  return ret;
}

int C(int n, int k) {
  return (ll) fac[n] * ifac[k] % mod * ifac[n - k] % mod;
}

int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(0);
  
  int n, k;
  std::cin >> n >> k;

  fac[0] = 1;
  for (int i = 1; i <= n + 1; i++) {
    fac[i] = (ll) fac[i - 1] * i % mod;
  }
  ifac[n + 1] = power(fac[n + 1], mod - 2);
  for (int i = n; i >= 0; i--) {
    ifac[i] = (ll) ifac[i + 1] * (i + 1) % mod;
  }

  ll answer = 0;

  for (int i = 0; i <= k; i++) {
    if (i & 1) {
      answer -= (ll) C(n + 1, i) * power(k - i, n) % mod;
    } else {
      answer += (ll) C(n + 1, i) * power(k - i, n) % mod;
    }
  }

  answer += (ll) mod * mod;

  std::cout << answer % mod;
  
  return 0;
}

• Subtask 1: 4 / 4
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 51 / 51