제출 #1215256

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1215256		mychecksedad	Asceticism (JOI18_asceticism)	C++20	100 / 100	22 ms	16056 KiB

asceticism

/* Author : Mychecksdead  */
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define MOD (1000000000+7)
#define MOD1 (998244353)
#define pb push_back
#define all(x) x.begin(), x.end()
#define en cout << '\n'
#define ff first
#define ss second
#define pii pair<int,int>
#define vi vector<int>
const int N = 1e6+100, M = 1e5+10, K = 52, MX = 30;



ll f[N], rf[N];

ll po(ll a, ll b){ll res = 1; while(b){if(b&1) (res*=a)%=MOD; b>>=1; (a*=a)%=MOD;} return res;}

void precalc(){
    f[0] = 1;
    for(ll i = 1; i < N; ++i) f[i] = (f[i - 1] * i) % MOD;
    rf[N-1] = po(f[N-1], MOD-2);
    for(ll i = N-2; i >= 0; --i) rf[i] = (rf[i + 1] * (i+1)) % MOD;
}
ll c(ll n, ll k){
  if(n < k) return 0;
  return (((f[n] * rf[k]) % MOD) * rf[n - k]) % MOD;
}
ll n, k;
void solve(){
  precalc();
  cin >> n >> k;
  --k;
  ll ans = 0;
  for(int i = 0; i <= k; ++i){
    if(i % 2){
      ans -= c(n + 1, i) * (po(k + 1 - i, n)) % MOD;
    } else{
      ans += c(n + 1, i) * (po(k + 1 - i, n)) % MOD;
    } 
    ans %= MOD;
  }
  cout << (ans+MOD)%MOD;
}


int main(){
  cin.tie(0); ios::sync_with_stdio(0);
  int tt = 1, aa;
  // freopen("in.txt", "r", stdin);
  // freopen("out.txt", "w", stdout);
  while(tt--){
    solve();
    en;
  }
  cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" seconds\n";
  return 0;
} 

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