Submission #1231376

#	Time	Username	Problem	Language	Result	Execution time	Memory
1231376		tminh	Fancy Fence (CEOI20_fancyfence)	C++20	0 / 100	1 ms	328 KiB

fancyfence

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

#define ll long long
#define endl '\n'

const ll mod = 1e9 + 7;
const int N = 1e5 + 5;
const ll inv2 = 500000004;

int n;
ll h[N], w[N];
ll pre[N];
stack<int> s;
int l[N], r[N];

ll S(ll n) {
    n %= mod;
    ll res = n;
    res = (res * (n + 1)) % mod;
    res = (res * inv2) % mod;
    return res;
}

void solve() {
    pre[0] = 0;
    for (int i = 1; i <= n; ++i) {
        pre[i] = (pre[i - 1] + w[i]);
    }

    for (int i = 1; i <= n; ++i) {
        while (!s.empty() && h[s.top()] >= h[i]) s.pop();
        l[i] = (s.empty() ? 0 : s.top());
        s.push(i);
    }
    while (!s.empty()) s.pop();

    for (int i = n; i >= 1; --i) {
        while (!s.empty() && h[s.top()] >= h[i]) s.pop();
        r[i] = (s.empty() ? n + 1 : s.top());
        s.push(i);
    }

    ll ans = 0;
    for (int i = 1; i <= n; ++i) {
        ll W = (pre[r[i] - 1] - pre[l[i]]);
        
        ll prev_h = 0;
        if (l[i] > 0) prev_h = max(prev_h, h[l[i]]);
        if (r[i] <= n) prev_h = max(prev_h, h[r[i]]);
        
        ll count_W = S(W);
        ll count_H_total = S(h[i]);
        ll count_H_prev = S(prev_h);
        ll count_H_new = (count_H_total - count_H_prev + mod) % mod;
        
        ll contribution = (count_W * count_H_new) % mod;
        ans = (ans + contribution) % mod;
    }
    cout << ans << endl;
}

void input() {
    cin >> n;
    for (int i = 1; i <= n; ++i) cin >> h[i];
    for (int i = 1; i <= n; ++i) cin >> w[i];
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    input();
    solve();

    return 0;
}

• 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