Submission #1282913

#	Time	Username	Problem	Language	Result	Execution time	Memory
1282913		red_souls	Fancy Fence (CEOI20_fancyfence)	C++20	0 / 100	1 ms	580 KiB

fancyfence

#include <bits/stdc++.h>
#define ll long long
#define task "Histogram"
using namespace std;

const int N = 1e5 + 16;
const ll INF = 1e18, mod = 1e9 + 7;
int n;
ll w[N], h[N];

namespace sub6 {

    ll result, prefix[N];

    stack <int> st;
    int L[N], R[N];

    ll sqr(ll k) {
        return k * k % mod;
    }

    ll powMod(ll a, ll b) {
        if (b == 0) {
            return 1;
        }
        if (b & 1) {
            return a * (sqr(powMod(a, b >> 1)) % mod) % mod;
        }
        return sqr(powMod(a, b >> 1)) % mod;
    }

    ll inv2, inv6;

    void solve() {
        inv2 = powMod(2, mod - 2);
        inv6 = powMod(6, mod - 2);

        while (!st.empty()) {
            st.pop();
        }
        for (int i = 1; i <= n; i++) {
            while (!st.empty() && h[st.top()] >= h[i]) {
                st.pop();
            }
            if (st.empty()) {
                L[i] = 1;
            }
            else {
                L[i] = st.top() + 1;
            }
            st.push(i);
        }

        while (!st.empty()) {
            st.pop();
        }
        for (int i = n; i >= 1; i--) {
            while (!st.empty() && h[st.top()] > h[i]) {
                st.pop();
            }
            if (st.empty()) {
                R[i] = n;
            }
            else {
                R[i] = st.top() - 1;
            }
            st.push(i);
        }

        for (int i = 1; i <= n; i++) {
            prefix[i] = prefix[i - 1] + w[i];
        }

        for (int i = 1; i <= n; i++) {

            ll A = prefix[L[i]];
            ll B = prefix[n] - prefix[R[i]];

            ll s = w[i] * A % mod * B % mod;
            ll c1 = ((w[i] * (w[i] - 1) % mod) * inv2) % mod;
            ll c2 = ((w[i] * (w[i] + 1) % mod) * inv2) % mod;
            ll c3 = (w[i] * (w[i] + 1) % mod * (w[i] - 1) % mod) % mod * inv6 % mod;

            s = (s + A * c1 % mod) % mod;
            s = (s + B * c2 % mod) % mod;
            s = (s + c3) % mod;

            ll z = h[i] * (h[i] + 1) % mod * inv2 % mod;

            result = (result + s * z % mod) % mod;
        }
        cout << result;
    }
}

int main() {
    ios_base :: sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    if (fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }

    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> h[i];
    }
    for (int i = 1; i <= n; i++) {
        cin >> w[i];
    }
    sub6 :: solve();

    return 0;
}

Compilation message (stderr)

fancyfence.cpp: In function 'int main()':
fancyfence.cpp:102:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  102 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
fancyfence.cpp:103:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  103 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• 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