Codeforces Round #622 (Div. 2) C. Skyscrapers

https://codeforces.com/contest/1313/problem/C2

單調棧維護下每一個位置向前向後單調的最大和

const int maxn = 5e5 + 7;
 
#define int long long
int n, t, m;
 
int a[maxn], pre[maxn], suf[maxn];
stack<pair<int, int>> st;
 
void solve() {
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
 
    for (int i = 1; i <= n; i++) {
        if (st.size() == 0 || a[i] > st.top().first) {
            st.push({a[i], 1});
            pre[i] = pre[i - 1] + a[i];
        } else {
            pair<int, int> nex = {a[i], 1};
            pre[i] = pre[i - 1] + a[i];
            while (st.size() && st.top().first > a[i]) {
                auto tp = st.top();
                st.pop();
                pre[i] -= (tp.first - a[i]) * tp.second;
                nex.second += tp.second;
            }
            st.push(nex);
        }
    }
    while (st.size()) st.pop();
    for (int i = n; i >= 1; i--) {
        if (st.size() == 0 || a[i] > st.top().first) {
            st.push({a[i], 1});
            suf[i] = suf[i + 1] + a[i];
        } else {
            pair<int, int> nex = {a[i], 1};
            suf[i] = suf[i + 1] + a[i];
            while (st.size() && st.top().first > a[i]) {
                auto tp = st.top();
                st.pop();
                suf[i] -= (tp.first - a[i]) * tp.second;
                nex.second += tp.second;
            }
            st.push(nex);
        }
    }
    int ans = 0, pl = 0;
    for (int i = 1; i <= n; i++)
        if (suf[i] + pre[i] - a[i] > ans)
            ans = suf[i] + pre[i] - a[i], pl = i;
    for (int i = pl + 1; i <= n; i++)
        a[i] = min(a[i], a[i - 1]);
    for (int i = pl - 1; i >= 1; --i)
        a[i] = min(a[i], a[i + 1]);
    for (int i = 1; i <= n; i++)
        cout << a[i] << " ";
}