Submission #577528

#	Time	Username	Problem	Language	Result	Execution time	Memory
577528		tengiz05	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	25 ms	3060 KiB

fancyfence

#include <bits/stdc++.h>

using namespace std;
using i64 = long long;

constexpr int P = 1E9 + 7, D = (P + 1) / 2;

i64 norm(i64 x) {
    if (x < 0)
        x += P;
    else if (x >= P)
        x -= P;
    return x;
}

i64 C(i64 x) {
    x = norm(x);
    return x * (x + 1) % P * D % P;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int n;
    cin >> n;
    
    vector<i64> h(n + 1), w(n + 1);
    for (int i = 1; i <= n; i++) {
        cin >> h[i];
    }
    for (int i = 1; i <= n; i++) {
        cin >> w[i];
        w[i] += w[i - 1];
        w[i] %= P;
    }
    
    vector<i64> s{0};
    i64 sum = 0;
    
    i64 ans = 0;
    
    for (int i = 1; i <= n; i++) {
        while (h[s.back()] > h[i]) {
            i64 height = h[s.back()];
            i64 r = w[s.back()];
            s.pop_back();
            i64 l = w[s.back()];
            sum = norm(sum - (r - l) * C(height) % P);
            sum = norm(sum + (r - l) * C(h[i]) % P);
        }
        ans = norm(ans + sum * (w[i] - w[i - 1]) % P);
        ans = norm(ans + C(w[i] - w[i - 1]) * C(h[i]) % P);
        sum = norm(sum + (w[i] - w[i - 1]) * C(h[i]) % P);
        s.push_back(i);
    }
    
    cout << ans << "\n";
    
    return 0;
}

• 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