Submission #721428

#	Time	Username	Problem	Language	Result	Execution time	Memory
721428		d4xn	Fancy Fence (CEOI20_fancyfence)	C++17	0 / 100	1 ms	364 KiB

fancyfence

#pragma GCC optimize ("Ofast")
#include <bits/stdc++.h>
using namespace std;

#define int long long

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

int n, w[N], pre[N];
pair<int, int> v[N];
set<int> st;

int pw(int x, int y) {
  return (!y ? 1 : pw(x*x % mod, y/2) * (y%2 ? x : 1) % mod);
}

int inv(int x) {
  return pw(x, mod-2);
}

signed main() {
  ios::sync_with_stdio(false); cin.tie(nullptr);

  cin >> n;
  for (int i = 0; i < n; i++) {
    int h;
    cin >> h;
    v[i].first = h;
    v[i].second = i;
  }
  sort(v, v+n);  

  for (int i = 0; i < n; i++) {
    cin >> w[i];
    pre[i] = w[i] + (i ? pre[i-1] : 0);
  }

  int ans = 0;
  int inv2 = inv(2);
  for (int i = 0; i < n; i++) {
    int h = v[i].first;
    int idx = v[i].second;
    auto it = st.upper_bound(idx);

    int l = 0;
    if (it != st.begin()) l = *prev(it) + 1;

    int r = n-1;
    if (it != st.end()) r = *it - 1;

    int szL = pre[idx] - (l ? pre[l-1] : 0);
    int szR = pre[r] - pre[idx];
    ans += szL * szR % mod * h % mod * (h-1) % mod * inv2 % mod;
    ans %= mod;
    ans += szL * szR % mod * h % mod;
    ans %= mod;

    szL = (idx ? pre[idx-1] : 0) - (l ? pre[l-1] : 0);
    szR = pre[r] - (idx ? pre[idx-1] : 0);
    ans += szL * szR % mod * h % mod * (h-1) % mod * inv2 % mod;
    ans %= mod;
    ans += szL * szR % mod * h % mod;
    ans %= mod;

    ans += w[idx] * (w[idx]-1) % mod * inv2 % mod * h % mod * (h-1) % mod * inv2 % mod;
    ans %= mod;
    ans += w[idx] * (w[idx]-1) % mod * inv2 % mod * h % mod;
    ans %= mod;

    ans += w[idx] * h % mod * (h-1) % mod * inv2 % mod;
    ans %= mod;
    ans += w[idx] * h % mod;
    ans %= mod;

    st.insert(idx);
  }
  cout << ans << "\n";
}

• Subtask 1: 0 / 0
• Subtask 2: 0 / 12
• Subtask 3: 0 / 13
• Subtask 4: 0 / 15
• Subtask 5: 0 / 15
• Subtask 6: 0 / 18
• Subtask 7: 0 / 27