Submission #65881308

Source Code Expand

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#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    vector<int> P(N + 2), inc(N + 2), type(N + 2);
    for (int i = 1; i <= N; i++) cin >> P[i];
    for (int i = 1; i < N; i++)
        inc[i] = (P[i] < P[i + 1]);
    vector<int> extrema;
    for (int i = 2; i < N; i++) {
        if (P[i - 1] < P[i] && P[i] > P[i + 1]) {
            extrema.push_back(i);
            type[i] = 1;
        } else if (P[i - 1] > P[i] && P[i] < P[i + 1]) {
 
 
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#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    vector<int> P(N + 2), inc(N + 2), type(N + 2);
    for (int i = 1; i <= N; i++) cin >> P[i];

    for (int i = 1; i < N; i++)
        inc[i] = (P[i] < P[i + 1]);

    vector<int> extrema;
    for (int i = 2; i < N; i++) {
        if (P[i - 1] < P[i] && P[i] > P[i + 1]) {
            extrema.push_back(i);
            type[i] = 1;
        } else if (P[i - 1] > P[i] && P[i] < P[i + 1]) {
            extrema.push_back(i);
            type[i] = 2;
        }
    }

    vector<ll> prefix_sum(N + 2), weighted_sum(N + 2);
    for (int i = 1; i <= N; i++) {
        prefix_sum[i] = prefix_sum[i - 1] + inc[i];
        weighted_sum[i] = weighted_sum[i - 1] + (ll)inc[i] * i;
    }

    ll result = 0;
    int M = extrema.size();

    for (int i = 0; i + 1 < M; i++) {
        int a = extrema[i], b = extrema[i + 1];
        if (type[a] == type[b]) continue;

        int L = (i > 0 ? extrema[i - 1] : 1), R = a - 1, U = (i + 2 < M ? extrema[i + 2] : N);
        if (R < L || U <= b) continue;

        int R1 = min(R, b - 2);
        if (R1 >= L)
            result += (prefix_sum[R1] - prefix_sum[L - 1]) * (U - b);

        int l = max(L, b - 1), r = min(R, U - 3);
        if (r >= l)
            result += (ll)(U - 2) * (prefix_sum[r] - prefix_sum[l - 1])
                    - (weighted_sum[r] - weighted_sum[l - 1]);
    }
    cout << result << "\n";
    return 0;
}

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