Submission #305542

#	Time	Username	Problem	Language	Result	Execution time	Memory
305542		quocnguyen1012	Asceticism (JOI18_asceticism)	C++14	100 / 100	21 ms	1152 KiB

asceticism

#include <bits/stdc++.h>

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define ar array

using namespace std;
typedef long long ll;
typedef pair<int, int> ii;

const int mod = 1e9 + 7, maxn = 1e5 + 5;

int fact[maxn], ifact[maxn];
int N, K;

int power(int a, int b) {
  if (b == 0) return 1;
  int res = power(a, b / 2);
  if (b & 1) return (ll)res * res % mod * a % mod;
  return (ll)res * res % mod;
}

int inv(int a) {
  return power(a, mod - 2);
}

int binom(int k, int n) {
  if (k < 0 || n < 0 || k > n) return 0;
  return (ll)fact[n] * ifact[k] % mod * ifact[n - k] % mod;
}

void add(int & x, int y) {
  x += y;
  if (x >= mod) x -= mod;
  if (x < 0) x += mod;
}

signed main(void) {
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  #ifdef LOCAL
    freopen("A.INP", "r", stdin);
    freopen("A.OUT", "w", stdout);
  #endif // LOCAL

  fact[0] = 1;
  for (int i = 1; i < maxn; ++i) {
    fact[i] = (ll)fact[i - 1] * i % mod;
  }
  ifact[maxn - 1] = inv(fact[maxn - 1]);
  for (int i = maxn - 2; i >= 0; --i) {
    ifact[i] = (ll)ifact[i + 1] * (i + 1) % mod;
  }

  cin >> N >> K;
  int res = 0;
  for (int i = 0; i <= K; ++i) {
    int sign = 1;
    if (i & 1) sign = -1;
    int way = (ll)power(K - i, N) * binom(i, N + 1) % mod;
    ///cerr << way << '\n';
    add(res, sign * way);
  }
  cout << res;
}

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