Submission #128244

#	Time	Username	Problem	Language	Result	Execution time	Memory
128244		RockyB	Asceticism (JOI18_asceticism)	C++17	100 / 100	42 ms	1144 KiB

asceticism

#include <bits/stdc++.h>

#define f first
#define s second

#define pb push_back
#define pp pop_back

#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()

#define rep(a, b, c) for (int a = (b); (a) <= (c); ++a)
#define per(a, b, c) for (int a = (b); (a) >= (c); --a) 

#define nl '\n'
#define ioi exit(0);

using namespace std;

typedef long long ll;

const int MAX_N = (int)1e5 + 7;
const int mod = (int)1e9 + 7;


int n, k;


int f[MAX_N], rv[MAX_N];

int bp(int x, int y) {
  int res = 1;
  while (y) {
    if (y & 1) res = res * 1ll * x % mod;
    x = x * 1ll * x % mod, y >>= 1;
  }
  return res;
}

int cnk(int x, int y) {
  return ((f[x] * 1ll * rv[x - y]) % mod) * 1ll * rv[y] % mod;
}
int main() {
  #ifdef IOI
    freopen ("in.txt", "r", stdin);
  #endif
  cin >> n >> k;
  /* rep(i, 0, n + 1) {
    c[i][0] = 1;
    rep(j, 1, i) {
      c[i][j] = (c[i - 1][j] + c[i - 1][j - 1]) % mod;
    }
  } */
  f[0] = rv[0] = 1;
  rep(i, 1, n + 1) {
    f[i] = f[i - 1] * 1ll * i % mod;
    rv[i] = bp(f[i], mod - 2);
  }

  int ans = 0;
  k--;
  rep(i, 0, k) {
    int x = bp(-1, i) * 1ll * cnk(n + 1, i) % mod;
    x = x * 1ll * bp(k - i + 1, n) % mod;
    ans += x;
    ans %= mod;
    ans += mod;
    ans %= mod;
  }
  cout << ans;
    //cout << dp[n][k];
  ioi
}

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