제출 #1121051

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1121051		fryingduc	Cryptography (NOI20_crypto)	C++17	100 / 100	120 ms	8176 KiB

Crypto

#include "bits/stdc++.h"
using namespace std;

#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif

const int maxn = 3e5 + 5;
const int mod = 1e9 + 7;
int n, a[maxn];
int bit[maxn];
int fact[maxn];
int add(int x, int y) {
  if(y < 0) y += mod;
  x = x + y;
  if(x >= mod) x -= mod;
  return x;
}
void update(int i, int val) {
  for(; i <= n; i += i & (-i)) {
    bit[i] += val;
  }
}
int get(int i) {
  int ans = 0;
  for(; i > 0; i -= i & (-i)) {
    ans += bit[i];
  }
  return ans;
}
void solve() {
  cin >> n;
  vector<int> vec;
  fact[0] = 1;
  for(int i = 1; i <= n; ++i) {
    cin >> a[i];
    fact[i] = 1ll * fact[i - 1] * i % mod;
    vec.push_back(a[i]);
  }
  sort(vec.begin(), vec.end());
  for(int i = 1; i <= n; ++i) {
    a[i] = lower_bound(vec.begin(), vec.end(), a[i]) - vec.begin() + 1;
    update(a[i], 1);
  }
  int ans = 1;
  for(int i = 1; i <= n; ++i) {
    ans = add(ans, 1ll * get(a[i] - 1) * fact[n - i] % mod);
    update(a[i], -1);
  }
  cout << ans;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  solve();

  return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 9 / 9
• Subtask 3: 10 / 10
• Subtask 4: 11 / 11
• Subtask 5: 21 / 21
• Subtask 6: 13 / 13
• Subtask 7: 19 / 19
• Subtask 8: 12 / 12