Submission #782515

#	Time	Username	Problem	Language	Result	Execution time	Memory
782515		t6twotwo	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	27 ms	4184 KiB

fancyfence

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
constexpr int mod = 1e9 + 7;
constexpr int i2 = 500000004;
constexpr int i6 = 166666668;
int mul(int a, int b) {
    return 1LL * a * b % mod;
}
void add(int &a, int b) {
    a += b;
    if (a >= mod) {
        a -= mod;
    }
}
void sub(int &a, int b) {
    a -= b;
    if (a < 0) {
        a += mod;
    }
}
int f(int n) {
    return mul(i2, mul(n, n + 1)); 
} 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    vector<int> h(N), w(N); 
    for (int &x : h) {
        cin >> x;
    }
    for (int &x : w) {
        cin >> x;
    }
    int ans = 0, s = 0;
    vector<array<int, 2>> stk;
    for (int i = 0; i < N; i++) {
        add(ans, mul(f(h[i]), f(w[i])));
        int t = w[i];
        while (!stk.empty() && stk.back()[0] >= h[i]) {
            sub(s, mul(f(stk.back()[0]), stk.back()[1]));
            add(t, stk.back()[1]);
            stk.pop_back();
        }
        add(s, mul(f(h[i]), t));
        add(ans, mul(w[i], s));
        sub(ans, mul(f(h[i]), mul(w[i], w[i])));
        stk.push_back({h[i], t});
    }
    cout << ans << "\n";
    return 6/22;
}

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